Formable light weight composites

ABSTRACT

The present invention relates to light weight composite materials which comprise a metallic layer and a polymeric layer, the polymeric layer containing a filled thermoplastic polymer which includes a thermoplastic polymer and a metallic fiber. The composite materials of the present invention may be formed using conventional stamping equipment at ambient temperatures. Composite materials of the present invention may also be capable of being welded to other metal materials using a resistance welding process such as resistance spot welding.

CLAIM OF BENEFIT OF FILING DATE

The present application claims the benefit of the filing date of U.S.Provisional Patent Application Nos. 61/089,704 (filed on Aug. 18, 2008)and 61/181,511 (filed on May 27, 2009), “Formable Light WeightComposites”, by Shimon Mizrahi), the contents of which are herebyincorporated by reference in their entirety.

FIELD OF THE INVENTION

The present invention relates generally to composite materials, and moreparticularly to sandwich composites that include a fiber-filledpolymeric layer and a metallic layer.

BACKGROUND

Light weight composites which have a good balance of high stiffness,high toughness, and low weight are used in many applications whichrequire low flexibility and can benefit by reduced part weight.Transportation is one industry which has a need for such materials, forexample, as a component of a vehicle or for an object (such as acontainer) which is being transported.

The oil crisis in the late 1970s and early 1980s prompted development oflow weight laminates of metal sheets and polymers. Some of the theseefforts are reviewed by Kim et al. (Jang-Kyo Kim and Tong-Xi Yu,“Forming and Failure Behavior of Coated, Laminated and Sandwiched SheetMetal: A Review”, J. Mater. Process. Technology 63:33-42, 1997). Intheir review, Kim et al. describe the use of composites containing steelfaces and either nylon 6 or polypropylene cores of thickness of0.2/0.4/0.2 mm for automotive body panels. This kind of sandwich hasexceptional high flexural strength to weight ratio thus leading also toits successful implementation in many engineering applications (Mohr andStraza, 2005). However, specific technical problems must be solved whenthin sandwich sheets for the automotive industry are concerned. Theseproblems are related to what is required to adapt such sandwiches tomass production, especially low cost forming processes, such as thealready existing stamping processes (and particularly using existingstamping equipment). The ability to use standard stamping lines willreduce capital costs, increase versatility of existing equipment, reducetransition and implementation times, and circumvent major difficultiesrelated to unconventional sandwich-specific manufacturing techniques.

As far as the development of very thin sandwich sheets is concerned, twomajor approaches have been pursued. The first approach is a group of allmetal sandwiches of thin metal skins and a metallic cellular core.Generally, this group can be welded similarly to a typical weldablemetal sheet, since it tends to conduct electricity. The second approach,however, typically has two faces of thin metal sheets, separated by acentral polymer core layer (which typically are relatively softviscoelastic materials), and is structured so that it does not conductelectricity across the core layer largely due to the insulative andnon-conductive nature of the polymer core layer. The polymeric materialin any core of this structure may in fact be an insulator. Thus suchsandwich sheet may not be joined by spot welding or require weldingconditions (e.g., force, current, cycles, weld time) that may besubstantially greater than required for sheet metal having the samethickness. When weldability is concerned, the all metallic sandwich is,therefore, preferred.

Gissinger et al. (1994, U.S. Pat. No. 5,347,099) discloses a methodusing a specific arrangement of rollers and partially overlappingsandwich sheets as a possible approach to facilitate welding.

Straza (International Patent Application Publication No. WO2007/062061)discloses a method of manufacturing a metal core sandwich structure of acellular metal core having a shape selected from a group consisting of:octagons, hexagons, pentagons, squares, rectangles, triangles, andcircles. Clyne et al. (2004, U.S. Pat. No. 6,764,772) describe asandwich material of two metal plates which are affixed to and separatedby a fibrous metal core that is generally exposed to air, whereinsubstantially all of the fibers are inclined at an acute angle to theplates. However, one possible difficulty with those specific cellularmetal cores is that the structure is not continuous and thus the facesheet is not supported over the length of the cell. In case of soft facesheets, the thin cell walls may be damaged locally. Their applicationsthus tend to be limited. It is also a costly structure in that itgenerally requires the use of expensive materials for resistingcorrosion.

Typically, the formability of some metal composites has been found to beinferior to corresponding homogeneous sheet metal of the same thickness.The composites have limited drawing ratios and a higher tendency towrinkle as well as several potential geometrical defects in bending. Forsome materials, these defects may be the result of large sheardeformations in the interlayer because the core material is weakcompared to the sheet metal. Another possible vulnerability of manycomposites (e.g. sandwiches or laminates), may be their susceptibilityto dents. Wrinkling may be attributed to low yield strength of the corematerial.

Kim et al. (2003) tested the formability of a certainAluminum/Polypropylene/Aluminum sandwich sheets as a possible materialfor automotive usage. Their analysis suggested that certainpolypropylene cores may result in sandwich sheets having improvedformability.

Efforts in the art to modify polymeric cores of sandwich composites byintroducing a fibrous phase generally have produced the effect ofrestricting the elongation and thus decreasing the ductility of thecomposite material. Accordingly, such materials have not been givenconsiderable attention for a stampable composite.

Efforts in the art to enhance welding of sandwich composites generallyhave been directed at modifying polymeric cores of the sandwichcomposites by loading them with relatively large amounts of conductiveparticle fillers.

Thus, there still exists a need for light weight composite materialswhich have improved formability over the existing materials. As such,there is a need for sandwich sheets or laminates which have improvedductility so that low-cost standard sheet metal forming technology couldbe employed.

Also, there continues to exist a need for a weldable light weightcomposite having a polymeric layer that does not impede weldability. Theability to join a composite part to other metal containing parts, inparticular by welding (e.g., by a resistance welding technique, such asspot welding) is highly desirable.

Additionally, there is a need for light weight composites that can beprocessed to form an outer covering layer (e.g., to form one or both ofa decorative covering, or functional covering, such as a functionalcoating to improve bonding of the surface to another material such as anadhesive).

SUMMARY OF THE INVENTION

One or more of the above needs may be met with a light weight compositecomprising a first metallic layer; a polymeric layer disposed on thefirst layer; and a metallic fiber distributed within the polymericlayer; wherein the polymeric layer includes a polymeric materialcontaining a polymer, the polymer having an elongation at failure of atleast about 20% at a tensile strain rate of about 0.1 s⁻¹ as measuredaccording to ASTM D638-08; so that the resulting composite material maybe welded (e.g., by an art disclosed resistance welding method),plastically deformed at strain rates greater than about 0.1 s⁻¹ (e.g.,so that it can be stamped by an art disclosed metal stamping operationwithout rupture, delamination, and/or splitting), or both. Morepreferably, the polymeric layer is sandwiched between the first metalliclayer and a second metallic layer.

This aspect of the invention may be further characterized by one or anycombination of the following features: the polymer includes athermoplastic polymer having a glass transition temperature, T_(g),greater than about 80° C., or a melting temperature, T_(m), greater thanabout 80° C.; the volume ratio of the polymer (e.g., the thermoplasticpolymer) to the metallic fiber is greater than about 2.2:1 (preferablygreater than about 2.5:1, and more preferably greater than about 3:1);the composite comprises a second metallic layer, such that the polymericlayer is a core layer interposed between the first metallic layer andthe second metallic layer; the thermoplastic polymer includes a polymerselected from the group consisting of polypropylene, acetal copolymers,polyamides, polyamide copolymers, polyimides, polyester, polycarbonates,ABS polymer (acrylonitrile/butadiene/styrene copolymer), polystyrenes,ethylene copolymers including at least 80 wt. % ethylene, and any blendor combination thereof; the thermoplastic polymer comprises a polymerhaving a crystallinity from about 20% to about 80%; the filledthermoplastic polymer is characterized by an extrapolated yield stress,Y, and a strain hardening modulus, G, measured at a strain rate of 0.1s⁻¹, wherein the ratio Y/G is less than about 9 (e.g., less than about3); the filled thermoplastic polymer is characterized by a strainhardening modulus, G, which is greater than about 1 MPa; the filledthermoplastic polymer is characterized by an extrapolated yield stress,Y, which is less than about 120 MPa, a tensile modulus greater thanabout 750 MPa, a tensile strength of at least about 25 MPa, or anycombination thereof; the thermoplastic polymer comprises an elastomermodified polymer; the thermoplastic polymer is substantially free of anyplasticizer; the metallic fiber is uniformly distributed within thepolymeric layer; the metallic fiber is selectively located within thepolymeric layer; the metallic fibers are characterized by a weightaverage length greater than about 1 mm; the metallic fibers arecharacterized by a weight average diameter from about 1.0 μm to about 50μm; the filler further comprises a metallic particle having a weightaverage particle size less than about 0.10 mm; the filler furthercomprises a filler particle selected from a carbon black, graphite, ironphosphide or a combination thereof, and the filler particle is presentat a concentration less than about 5 volume %, based on the total volumeof the core layer; the metallic fiber is selected from the groupconsisting of steel, stainless steel, aluminum, magnesium, titanium,copper, alloys containing at least 40 wt % copper, alloys containing atleast 40 wt % iron, alloys containing at least 40 wt % aluminum, alloyscontaining at least 40 wt % titanium, and any combination thereof; themetallic fiber concentration is less than about 20 volume % based on thetotal volume of the polymeric layer; the filler includes reclaimedmetallic particles or reclaimed metallic fibers which are produced fromoffal recovered from a stamping operation; the first metallic layercomprises a first metallic material selected from the group consistingof steel, high strength steel, medium strength steel, ultra-highstrength steel, titanium, aluminum, and aluminum alloys; the secondmetallic layer comprises a second metallic material selected from thegroup consisting of steel, high strength steel, medium strength steel,ultra-high strength steel, titanium, aluminum, and aluminum alloys,wherein the first metallic material and the second metallic material aremade of the same metallic material; the second metallic layer comprisesa second metallic material selected from the group consisting of steel,high strength steel, medium strength steel, ultra-high strength steel,titanium, aluminum, and aluminum alloys, wherein the first metallicmaterial and the second metallic material are made of different metallicmaterials; the composite comprises a plurality of metallic layers, aplurality of polymeric layers, or both; the composite comprises a thirdmetallic layer interposed between two polymeric layers, wherein thethird metallic layer is perforated; the composite is i) substantiallyfree of epoxy, ii) substantially free of polymeric fibers, iii)substantially free of an adhesive layer interposed between the polymericlayer and the first metallic layer, iv) or any combination of (i)through (iii); the composite includes an adhesive layer interposedbetween the polymeric layer and the first metallic layer, wherein theadhesive layer includes a metallic fiber, a conductive filler particleselected from the group consisting of metallic particles, metallicfiber, carbon black, graphite, iron phosphide, or any combinationthereof, or both; or the composite is capable of a draw ratio of atleast 1.5 in a stamping operation.

Another aspect of the invention is directed at a method formanufacturing a composite material, such as a composite materialdescribed above, comprising the step of i) depositing the metallic fiberand the polymer for forming the polymeric layer that is bonded on thefirst metallic layer.

This aspect of the invention may further be characterized by one or anycombination of the following features: the polymeric layer is bondeddirectly to the first metallic layer; the process includes the steps ofheat bonding the polymeric layer to the first metallic layer, andapplying a pressure to the polymeric layer and the first metallic layer,wherein the heat bonding step includes heating at least a portion of thepolymeric layer in contact with the first metallic layer to atemperature greater than T_(min), wherein T_(min) is the higher of themaximum melting temperature (as measured by differential scanningcalorimetry at a heating rate of 10° C./min) of the one or more polymersof the filled thermoplastic material and the maximum glass transitiontemperature of the one or more polymer of the filled thermoplasticmaterial; the process further comprises a step of bonding a secondmetallic layer to the polymeric layer, such that the polymeric layerforms a core layer interposed between the first and second metalliclayers; the process further comprises a step of extruding an admixtureincluding the metallic fibers and the one or more polymers in anextruder at a temperature greater than T_(min); the process includes astep of providing at least some of the metallic fibers to the extruderas a pre-compounded filled polymeric particle that includes metallicfibers formed by a pultrusion step, wherein the pultrusion step includescoating a plurality of strands of metallic fiber with one or morepolymers, and chopping the coated strands to form particles of thefilled polymeric material containing the metallic fibers, such that themetallic fibers are oriented in the axial direction of the filledpolymeric material, wherein the concentration of the metallic fibers isgreater than about 1 volume % based on the total volume of the filledpolymeric material; the metallic fibers are chopped metallic fibers; themetallic fibers are provided to the one or more openings in the extruderas chopped fibers; the process includes a step of recycling or reusingthe composite material; the first and second metallic layers areprovided as rolls of metallic foil and the process is a continuousprocess including extruding the filled thermoplastic material at atemperature greater than T_(min), contacting the first and secondmetallic layers to opposing surfaces of the filled thermoplasticmaterial occurs prior to cooling the filled thermoplastic material to atemperature below T_(min); the step of applying pressure includes a stepof passing the composite material through at least one set ofcounter-rotating rollers, such that the thickness of the compositematerial is reduced by at least 2%.; the process includes a step ofplacing a spacer at least partially between the first and secondmetallic layers wherein the spacer is a solid at T_(min); a first partof the spacer is interposed between the first and second metallic layersand a second part of the spacer is not interposed between the first andsecond metallic layers, and the second part of the spacer has athickness greater than the thickness of the first part of the spacer;the process further includes a step of cleaning the first metalliclayer; the core layer includes from about 3 volume % to about 30 volume% metallic fiber based on the total volume of the core layer; the corelayer includes from about 5 volume % to about 25 volume % metallic fiberbased on the total volume of the core layer; the ratio of the volume ofthe one or more polymers to the volume of the metallic fibers is greaterthan about 2.2:1; the volume of the filled thermoplastic material is atleast 90% of the volume of the space between the first and secondmetallic layers; the composite material has a resistivity in thethrough-thickness direction of less than about 10,000 Ω·cm as measuredby the voltage drop between the two plates using AC modulation; theadmixture further comprises reclaimed metallic filler particle; whereinthe process includes a step of contacting the offal from a stampingoperation with a polymeric material to form the reclaimed metallicfiller particles; the reclaimed filler particles have a weight averageparticle diameter less than about 0.10 mm and have an aspect ratio lessthan about 10; the offal includes at least one offal layer which is ametallic material and at least one offal layer which contains athermoplastic material; the process includes a step of coating the firstsurface of the first metallic layer with a primer containing metallicparticles having an aspect ratio less than 10, an adhesive materialcontaining metallic particles having an aspect ratio less than 10, orboth; the first surface of the first metallic layer is free of both aprimer, an adhesive material, or both; the metallic fibers are randomlyarranged in the thermoplastic material (e.g., the ratio of the volume offibers in the direction in the plane of the core layer having thehighest concentration of fibers to the volume of fibers in theperpendicular direction is less than about 3:1, preferably less thanabout 2:1); the process includes a step of mixing metallic fibers andother filler particles; the process includes a step of chopping strandsof metallic fibers to form chopped fibers and feeding the chopped fibersinto an extruder, wherein the process is free of a step of placing thechopped fibers in a container; the process further comprises the stepsof: adhering a first surface of a second metallic layer to a firstsurface of a second filled thermoplastic material, contacting a secondsurface of the filled thermoplastic material that is adhered to thefirst metallic layer to a second surface of the filled thermoplasticmaterial that is adhered to the second metallic layer, such that the twofilled thermoplastic materials are interposed between the first andsecond metallic layers, and applying pressure to the second surfaces ofthe filled thermoplastic materials; wherein the second surface of thefilled thermoplastic material has a temperature greater than T_(min),such that the two filled thermoplastic materials adhere and form a corelayer interposed between the first and second metallic layers; or theprocess is characterized by T_(min) is greater than about 120° C.

Yet another aspect of the invention is directed at a method of forming acomposite part comprising the step of stamping a composite material,such as one described above, to form a part.

This aspect of the invention may be further characterized by one or anycombination of the following features: the process further comprising astep of coating at least one exterior surface of the composite material;the composite material is at a temperature less than about 45° C. duringthe stamping step; the stamping step includes a step of drawing at leastone portion of the composite material by a draw ratio greater than about1.5; the composite part is free of wrinkles, dents, and cracks; thecomposite part has a class A surface; the process further comprises astep of welding the composite material to at least one additional metalcontaining material, wherein the welding step is selected from groupconsisting of resistance welding, laser welding, and electron beamwelding; the welding step is a resistance welding step; the welding stepuses i) a welding current which is lower than the welding currentrequired to weld a monolithic metal sheet of the same material as thefirst metallic layer and having the same thickness as the compositematerial to the additional metal containing material, ii) a number ofweld cycles which is lower than the number of weld cycles required toweld a monolithic metal sheet of the same material as the first metalliclayer and having the same thickness as the composite material to theadditional metal containing material, or iii) both (i) and (ii); or thecomposite part is used in an automotive part selected from the groupconsisting of a bumper, a wheel house outer, a fender outer, a hoodouter, a front door outer, a rear door outer, a decklid outer, aliftgate outer, a back seat panel, a rear shelf panel, a dash cowall, arear compartment pan, a part having a tub for storage of a spare tire, apart having a tub for stow and go seating, a roof outer, a floor pan, abody side, or any combination thereof.

In another aspect, the invention is directed at the use a light weightcomposite materials, such as one described above, in an automotivepanel, a truck panel, a bus panel, a container, a panel on a train car,a panel in a jet, a bicycle tube, a motorcycle panel, a trailer panel, apanel on a recreational vehicle, or a panel on a snowmobile.

In still another aspect, the invention is directed at a weld jointcomprising: a first metallic layer having a first metal; ii) a secondmetallic layer having a second metal wherein the first metallic layer isin welded contact with the second metallic layer, an area of the weldedcontact defining a weld zone, and wherein the first metal and the secondmetal are the same or different; and a metallic ring at least partiallyencircling the weld zone, disposed between the first and second metalliclayers, and attached to the first, second, or both metallic layers inthe weld joint, wherein the metallic ring is of a metal that isdifferent from the first metal and the second metal.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A illustrates a composite material having a polymeric layer and ametallic layer.

FIG. 1B illustrates a composite material having a polymeric core layerinterposed between two metallic layers.

FIG. 2 is an example of one possible microstructure in accordance withthe present teachings in which a metallic fiber is distributed in acontinuous phase of a polymeric matrix.

FIG. 3A is an illustrative micrograph of a cross-section near a weldbetween a composite material and a sheet metal.

FIG. 3B is an illustrative micrograph of a cross-section near a weldbetween a composite material and a sheet metal.

FIG. 3C is an illustrative micrograph of a polymeric material includingmetallic fibers.

DETAILED DESCRIPTION

In general, the materials herein employ a filled polymeric material, aswill be described, and particularly one that includes a metal fiberphase distributed in a polymeric matrix. In general, the compositematerials herein employ at least two layers, one of which is the abovefilled (e.g., fiber-filled) polymeric material (e.g., in a fiber-filledpolymeric layer). More particularly, the materials herein are compositesthat include a sandwich structure, pursuant to which a fiber-filledpolymeric layer is sandwiched between two or more other layers. Thematerials herein also contemplate sandwich structure pre-cursors, e.g.,a first layer upon which a filled polymeric layer is attached so thatthe filled polymeric layer has an exposed outer surface. A second layermay subsequently be attached to the filled polymeric layer. Theinvention also contemplates feedstock compositions (e.g., in the form ofa pellet, a sheet, or otherwise) that include a fiber-filled polymericmaterial in accordance with the present teachings. As will beillustrated, the materials herein exhibit a unique, surprising, andattractive combination of properties, which render the materialssuitable for deforming operations (e.g., relatively high strain rateforming operations, such as stamping), welding operations, or both. Forinstance, as will be seen from the teachings, the filled polymeric layeris designed in a manner such that is multiphasic. At least one phase(e.g., the filler) provides a conductive flow path, and is such that itis plastically deformable, and may even strain harden when subjected toa stress that induces plastic deformation. In addition, the polymericphase is such that it bonds sufficiently to another material (e.g., ametal layer such as a steel sheet) that processing of the compositematerials for welding and/or deforming (e.g., forming, such as bystamping), will be free of delamination of the composite. The polymericphase may also be such that it withstands degradation when subjected tocoating operations (e.g., when subjected to chemical baths such aselectrostatic coating baths, or other baths for imparting corrosionresistance, common in sheet metal coating operations).

The present invention in its various aspects makes use of uniquecombinations of materials to derive an attractive composite, andparticularly a laminate composite. The laminate may be drawn (e.g., deepdrawn), welded, or both, in a manner similar to conventionalart-disclosed sheet materials, such as sheet metal (e.g., stainlessand/or low carbon steel). In general, the invention makes use of amulti-phase composite material in which the materials are selected andemployed so that, as a whole, they impart drawability, weldability, orboth. Additionally, the materials are such that the resulting laminatescan be processed in a manner similar to conventional art-disclosed thinwalled structures particularly as it relates to processes for impartinga decorative or functional surface treatment (e.g., a coating, aplating, or otherwise).

For example, a particular preferred combination of materials herein mayinclude two layers that flank a core material, the latter of which ispreferably a filled polymeric material. The filled polymeric materialpreferably includes at least one polymer, which polymer may include,consist essentially of, or consist entirely of a thermoplastic polymer,or otherwise has characteristics that render it generally processable asa thermoplastic polymer. The filled polymeric material preferably alsoincludes a filler phase, and preferably a phase having a filler thatincludes, consists essentially of, or consists entirely of a fiberphase, and particularly an elongated fiber phase, such as an elongatedmetal fiber phase. Such phase may be sufficiently positioned and/ordistributed (e.g., wrapped, braided, aligned, entangled, or anycombination thereof), and used in sufficient volume that an electricallyconductive network across at least portions of the filled polymericmaterial is realized even if the polymer itself generally is notconductive. A particularly preferred elongated fibrous phase may alsoitself exhibit elongation (either or both individual fibers or the massas a whole) and possibly strain hardening.

It should be appreciated that references to “layers” herein do notnecessarily require discrete and separate pieces of material. Forexample, a layered composite may still be within the teachings herein ifit includes a single sheet of a material that has been folded over uponitself to define two layers of the material, albeit sharing a commonedge, between which is located the filled polymeric material.

Turning now with more particularity to the teachings herein, it is seenthat in a first aspect there is contemplated a composite material thatis made from layers of adjoining dissimilar materials, which includes atleast one layer (e.g., a metal layer such as a metal face layer) and atleast one polymeric layer, the composite being formable (e.g., stampableby application of a stress to cause plastic strain (e.g., at arelatively rapid rate) of the material or otherwise capable of beingcold-formed on a press machine) into a formed panel. The compositematerial may be a composite laminate containing one metallic layer andone polymeric layer, or it may include one or more other layers. Forexample, it may be a laminate including one metallic layer interposedbetween two polymeric layers, or a laminate including a polymeric layersandwiched between at least two opposing metallic layers. As indicated,a particularly preferred approach envisions this latter structure, theformer structures possibly serving as precursors for the laterstructure. In such instance the method of forming a sandwich structuremay include a step of applying a layer to a precursor to form a sandwichstructure, a step of applying a first precursor to a second precursor toform a sandwich structure, or both.

An example of a composite laminate 10 having one metallic layer 14 andone polymeric layer 16 is illustrated in FIG. 1A. A sandwich 12 maycontain a first metallic layer 14, a second metallic layer 14′ and apolymeric layer 16 (e.g., a polymeric core layer) interposed between thefirst and second metallic layers, as illustrated in FIG. 1B. Referringto FIGS. 1A and 1B, the polymeric layer 16 includes at least one polymer(e.g., a thermoplastic polymer) 18 and a fiber 20. The polymeric layer16 and the first metallic layer 14 may have a common surface 22. Asillustrated in FIGS. 1A and 1B some or all of the fibers may have alength and orientation such that they extend from one surface of thepolymeric layer to the opposing surface of the polymeric layer. However,it will be appreciated that other fiber lengths and orientations arewithin the scope of the inventions. For example, the fraction of themetallic fibers that extend between the two opposing faces of thepolymeric layer may be less than 20%, less than 10%, less than 5%, orless than 1%.

As mentioned, in addition to the composite, multi-layered structures,another aspect of the invention contemplates a precursor polymeric layersheet material (i.e., a single layer of the polymeric layer) includingthe thermoplastic polymer and the fiber (e.g., metallic fiber), that canbe later sandwiched between two metallic layers.

Yet another aspect of the invention contemplates a precursor polymericfeedstock material containing the polymer and the fibers. Such apolymeric feedstock material may be formed (e.g., molded or extruded)into the polymeric layer (e.g., into a sheet) either as a singlematerial or by diluting with one or more additional materials (e.g., oneor more additional polymers). As such, the precursor polymeric feedstockmaterial may include some or all of the components in the polymericlayer of the composite material. Preferably, the precursor polymericfeedstock material includes substantially all of the fiber for thepolymeric layer.

In use, the composites may be deformed (e.g., formed, such as bystamping), attached to another structure (e.g., to steel or to anothercomposite material), or both. A preferred approach is to employ a stepof welding the composite of the invention to the other structure. Theformed panel may be joined to other parts, when necessary, by techniquesother than welding, such as by using adhesives, a brazing process, orthe like. In both cases, the composite material (e.g., the laminate orsandwich sheet) is formable by low-cost stamping methods and yet issurprisingly free of the limitations that have been faced previously inthe art. The unique features of the composite material render it anextremely attractive candidate for applications which traditionallyutilize a regular monolithic metal sheet, such as in the body panelscurrently employed in the transportation (e.g., automotive) industry.

One unique feature of the invention is that it includes specificselection of the polymer (e.g., thermoplastic polymer) and the metalfibers, and incorporation of metal fibers and optional particles, aswell as other fillers, into the polymeric matrix to produce a novelformable composite material (e.g. sandwich or laminate structure) forlow-cost stamping operation. Another novelty is that the stampablesandwiches can be joined by conventional welding techniques such asresistance welding (e.g., spot welding, seam welding, flash welding,projection welding, or upset welding), energy beam welding (e.g., laserbeam, electron beam, or laser hybrid welding), gas welding (e.g.,oxyfuel welding, using a gas such as oxyacetylene), arc welding (e.g.,gas metal arc welding, metal inert gas welding, or shielded metal arcwelding). Preferred joining techniques include high speed weldingtechniques such as resistance spot welding and laser welding.

Various features of formable/stampable materials such test methods, testcriteria, descriptions of defects, and descriptions of forming processesare described in the following publications, all expressly incorporatedherein by reference:

-   M. Weiss, M. E. Dingle, B. F. Rolfe, and P. D. Hodgson, “The    Influence of Temperature on the Forming Behavior of Metal/Polymer    Laminates in Sheet Metal Forming”, Journal of Engineering Materials    and Technology, October 2007, Volume 129, Issue 4, pp. 530-537.-   D. Mohr and G. Straza, “Development of Formable All-Metal Sandwich    Sheets for Automotive Applications”, Advanced Engineering Materials,    Volume 7 No. 4, 2005, pp. 243-246.-   J. K. Kim and T. X. Yu, “Forming And Failure Behaviour Of Coated,    Laminated And Sandwiched Sheet Metals: A Review”, Journal of    Materials Processing Technology, Volume 63, No 1-3, 1997, pp. 33-42.-   K. J. Kim, D. Kim, S. H. Choi, K. Chung, K. S. Shin, F.    Barlat, K. H. Oh, J. R. Youn, “Formability of    AA5182/polypropylene/AA5182 Sandwich Sheet, Journal of Materials    Processing Technology, Volume 139, Number 1, 20 Aug. 2003, pp. 1-7.-   Trevor William Clyne and Athina Markaki U.S. Pat. No. 6,764,772    (filed Oct. 31, 2001, issued Jul. 20, 2004).-   Frank Gissinger and Thierry Gheysens, U.S. Pat. No. 5,347,099, Filed    Mar. 4, 1993, Issued Sep. 13, 1994, “Method And Device For The    Electric Welding Of Sheets Of Multilayer Structure”.-   Straza George C P, International Patent Application Publication    (PCT): WO2007062061, “Formed Metal Core Sandwich Structure And    Method And System For Making Same”, Publication date: May 31, 2007.-   Haward R. N., Strain Hardening of Thermoplastics, Macromolecules    1993, 26, 5860-5869.

Materials

By way of example, the use of a fibrous filler in the polymeric layer isbelieved to facilitate composite manufacturing and surprisingly lowlevels may be employed to achieve the beneficial results herein.Surprisingly, the selection and combination of materials taught hereinaffords the ability to employ less metal per unit volume thanconventional metal structures of like form (e.g., sheet metal) whilestill exhibiting comparable properties and characteristics. The problemthat the skilled artisan might envision in such a combination ofmaterials unexpectedly are avoided. In this regard, some of thebehavioral characteristics of the materials that might be predicted aresurprisingly avoided, are employed advantageously in the resultingcomposite, or both. The resulting laminates thus render themselves asattractive candidates to be a drop-in substitute for existing materials,for example, they can be employed instead of sheet steel, without theneed for significant investment in resources to re-tool or significantlyalter processing conditions.

Polymeric Layer

The polymeric layer generally may include or even consist essentially ofa filled polymer, (e.g., a thermoplastic polymer filled with areinforcing fiber, such as a metallic fiber).

The filled polymeric material for use in the polymeric layer preferablyis one that generally would be characterized as being relatively rigid(i.e., has a relatively high stiffness, e.g., an apparent modulus ofrigidity of at least about 200 MPa as measured according to ASTMD1043-02, over a temperature range of about −40° C. to about 50° C.).The rigidity of the material may be sufficiently high so that it canprovide support for any layer between which it is disposed, such as thethin and soft face metal sheets (i.e., the metallic layers), the resultof which is that the composite material would be capable ofsubstantially supporting its own weight without sagging (e.g., a 10cm×10 cm sheet of the composite material having a thickness of betweenabout 0.5 and 2 mm, if clamped one cm deep along one edge to form acantilever having a free end opposing the clamped end would exhibit lessthan 5 mm deflection by the free end). Thus, the resulting compositewill be sufficiently rigid that it helps to resist deformations such asdents at relatively low impact forces, but will also deform generally ina plastic manner (similar to sheet metals) when subjected to crashimpact loads. For example, the filled polymeric material may have amodulus of rigidity (as measured according to ASTM D1043-02) greaterthan isotactic polypropylene, nylon 6, the polymer absent any filler(i.e. the same polymer as the used in the filled polymeric material, butwithout the metallic fiber and other filler as taught) or anycombination. Preferably the modulus of rigidity is at least 110%, morepreferably at least 125%, and most preferably at least 150% of themodulus of rigidity of the unfilled polymer (i.e. the same polymer asused in the filled polymeric material, but without the metallic fiberand other filler as taught). The filled polymeric material may have amodulus of rigidity greater than about 200 MPa, preferably greater thanabout 400 MPa, more preferably greater than about 800 MPa, even morepreferably greater than about 1500 MPa, and most preferably greater thanabout 2500 MPa.

Preferably, at least some of the polymer in the filled polymericmaterial is a thermoplastic, but it may be or include a thermosetpolymer, particularly a thermoset polymer that is processable as athermosplastic, but cured. Preferably, at least 50% (more preferably atleast 60%, 70%, 80%, 90% or even 95%, if not 100%) by weight of thepolymer used in the filled polymeric material is a thermoplasticpolymer.

The filled polymeric material may be characterized as being a relativelystrong polymeric material. For example, the filled polymeric materialmay have a relatively high tensile strength (as measured according toASTM D638-08 at a nominal strain rate of about 0.1 s⁻¹). The tensilestrength of the filled polymeric material may be greater than thetensile strength of the unfilled polymer (i.e. the same polymer as usedin the filled polymer, but without the metallic fiber and other filleras taught). Preferably the tensile strength is at least 110%, morepreferably at least 125%, and most preferably at least 150% of thetensile strength of the unfilled polymer (i.e. the same polymer as usedin the filled polymer, but without the metallic fiber and other filleras taught). The filled polymeric material may have a tensile strengthgreater than about 10 MPa, preferably greater than about 30 MPa, morepreferably greater than about 60 MPa, even more preferably greater thanabout 90 MPa, and most preferably greater than about 110 MPa.

The filled polymeric material may also be characterized as having arelatively high elongation at break. For example the filled polymericmaterial may be characterized by a percent elongation at break greaterthan 50%, preferably greater than 80% and most preferably greater thanabout 120%, as measured according to ASTM D638-08 at a nominal strainrate of about 0.1 s⁻¹.

The filled polymeric material may have high strain hardening properties(e.g., a ratio of Y/G less than about 9, more preferably less than about3, where Y is the extrapolated yield stress and G is the strainhardening modulus).

The filled polymeric material may have electrical conductivityproperties (e.g., the filled polymeric material may be an electricalconductor) such that the composite material may be welded to anotherstructure such as a sheet metal and a conductive path is providedthrough the filled polymer. The electrical conductivity properties ofthe polymeric core material may be achieved by employing metallic fibersand optionally metallic or carbon black particles that are dispersed inthe polymer in a quantity to have at least a percolation concentration(i.e., a minimum concentration at which a continuous network, orconductive path between the metal faces, is formed). For the teachingsherein, examples of preferred percolation concentrations may be between3-33% in volume (e.g., between 5-33%, between 10-30%, or even between3-12%) in volume based on the total volume of the filled polymericmaterial. Of course, higher concentrations may also be used. Thecomposite material may be weldable using art-disclosed weld schedules orwith such weld schedules having up to five additional weld cycles and/oran increase in the weld current by less then about 50%, and/or anincrease in the weld pressure by less than about 50%. It is unexpectedlyfound that the composite materials of the present invention may requirefewer weld cycles (e.g., at least 25% fewer weld cycles), a lower weldcurrent (e.g., at least 20% lower weld current), or both, to obtain agood weld, compared with the number of weld cycles and weld currentrequired to obtain a good weld from a monolithic metal sheet having thesame metal as a metal face on the composite and having the same totalthickness. Such welding conditions advantageously allow for moreeconomical weld schedules that are both faster and require less energy.

The filled polymeric material preferably is light weight and has adensity (as measured according to ASTM D792-00) at room temperature lessthan the density of the metal (assuming it is fully densified) of themetallic layer(s). The density of the filled polymeric material ispreferably less than 75%, more preferably less than 60%, even morepreferably less than 40% and most preferably less than 33% of thedensity of the metal of the metallic layer(s). By way of example, oneapproach herein envisions that the filled polymeric material (e.g.,including metallic fibers such as steel fibers) will have a density ofless than about 4 g/cm³, more preferably less than about 3.0 g/cm³,(e.g., the filled polymeric material may have a density in the range of1.2 to 2.8 g/cm³ or even 1.3 to 2.6 g/cm³)

The filled polymeric material (e.g., the polymer of the filled polymericmaterial) may additionally include one or more additives, such asantioxidants, stabilizers. lubricants, antiblocking agents, antistaticagents, coupling agents (e.g., for the fillers), foaming agents,pigments, flame retardant additives, and other processing aids known tothe polymer compounding art. Suitable flame retardants may includehalogen containing flame retardants and halogen free flame retardants.The flame retardant may also include an antimony containing compound,such as antimony oxide. Exemplary flame retardants which may be employedinclude chlorine containing flame retardants, bromine containing flameretardants, nitrogen containing flame retardant (such as melaminecyanurate), phosphorus containing flame retardants (such as phosphates,organophosphates, salts of phosphinic acids, and organophosphites),condensates of melamine with phosphoric acid or with condensedphosphoric acids (such as melamine phosphate, melam polyphosphate, melonpolyphosphate and melem polyphosphate), magnesium hydroxide (Mg(OH)₂)aluminium trihydrate (Al(OH)₃), and any combination thereof. Halogenatedflame retardant compounds which may be used include flame retardantsdisclosed in U.S. Pat. No. 3,784,509 (Dotson et. al., Jan. 8, 1974, seefor example the substituted imides described in column 1, line 59through column 4, line 64), U.S. Pat. No. 3,868,388 (Dotson et al.February 25, 1975, see for example the halogenated bisimides describedin column 1, line 23 through column 3, line 39); U.S. Pat. No. 3,903,109(Dotson et al. Sep. 2, 1975, see for example the substituted imidesdescribed in column 1, line 46 through column 4, line 50); U.S. Pat. No.3,915,930 (Dotson et al. Oct. 28, 1975, see for example halogenatedbisimides described in column 1, line 27 through column 3, line 40); andU.S. Pat. No. 3,953,397 (Dotson et al. Apr. 27, 1976, see for examplethe reaction products of a brominated imide and a benzoyl chloridedescribed in column 1, line 4 through column 2, line 28), each of whichis incorporated by reference in its entirety. If employed, the one ormore additives may be present at a concentration less than about 30 wt%, preferably less than about 20 wt. % and more preferably less thanabout 10 wt. %, based on the combined weight of the polymer andadditives.

The filled polymeric material may be free of a plasticizer or otherrelatively low molecular weight materials which may become volatilized(e.g., during a resistance welding process). If employed, theconcentration of plasticizer or other relatively low molecular weightmaterials preferably is less than about 3 wt. %, more preferably lessthan about 0.5 wt. %, and most preferably less than about 0.1 wt. %based on the total weight of the filled polymeric material (e.g., suchthat the filled polymeric material does not delaminate from a metalliclayer).

It is also possible the teachings herein contemplate a step of selectingmaterials, processing conditions, or both, so that during processing,delamination of the filled polymeric material from the metallic layer issubstantially, or entirely avoided (e.g., delamination caused by vaporpressure buildup at an interface between the filled polymeric materialand the metallic layer sufficient for causing delamination).

Polymers

With more attention now to particular examples of polymers for useherein, the polymers used for the filled polymeric material preferablyinclude thermoplastic polymers that either have a peak meltingtemperature (as measured according to ASTM D3418-08) or a glasstransition temperature (as measured according to ASTM D3418-08) greaterthan about 50° C. (preferably greater than about 80° C., even morepreferably greater than about 100° C., even more preferably greater thanabout 120° C., more preferably greater than about 160° C., even morepreferably greater than 180° C., and most preferably greater than about205° C.). The thermoplastic polymer may have a peak melting temperature,a glass transition temperature, or both that is less than about 300° C.,less than about 250° C., less than about 150° C., or even less thanabout 100° C. They may be at least partially crystalline at roomtemperature or substantially entirely glassy at room temperature.Suitable polymers (e.g., suitable thermoplastic polymers) may becharacterized by one or any combination of the following tensileproperties (measured according to ASTM D638-08 at a nominal strain rateof 0.1 s⁻¹): a tensile modulus (e.g., Young's Modulus) greater thanabout 30 MPa, (e.g., greater than about 750 MPa, or greater than about950 MPa); an engineering tensile strength (i.e., σ_(e)), a true tensilestrength (i.e., σ_(t), where at=(1+ε_(e))σ_(e) where ε_(e) is theengineering strain), or both, greater than about 8 MPa (e.g., greaterthan about 25 MPa, greater than about 60 MPa, or even greater than about80 MPa); or a plastic extension at break of at least about 20% (e.g., atleast about 50%, at least about 90%, or even at least about 300%).Unless otherwise specified, the term tensile strength refers toengineering tensile strength.

The polymer may preferably have a strain hardening properties that willbe characterized by a curve of tensile true stress (S_(t)) and aderivation of the polymer elongation having the form of: (L²−1/L) whereL is the extension ratio, namely the ratio between the final and theinitial length under tension (Haward R. N., Strain Hardening ofThermoplastics, Macromolecules 1993,26, 5860-5869). The curve is fittedby the equation:

S _(t) =Y+G(L ²−1/L)   (Equation 1)

where Y is the extrapolated yield stress and G is the strain hardeningmodulus. Polymers suitable for the filled polymeric material (e.g., apolymeric layer, such as a core layer in a sandwich composite herein)may have a relatively high strain hardening modulus, a relatively lowextrapolated yield stress, or both. The strain hardening modulus of thepolymer may be greater than about 1 MPa, preferably greater than about 2MPa, more preferably greater than about 4 MPa, and most preferablygreater than about 10 MPa. The extrapolated yield stress may be lessthan about 120 MPa, preferably less than about 80 MPa, and morepreferably less than about 30 MPa. The Y/G ratio preferably may be lessthan 9, preferably less than 3, and more preferably less than 2.

Examples of thermoplastic polymers which may be suitable for thepolymeric layer include polyolefins (e.g. polyethylene andpolypropylene), acetal copolymers, polyamides, polyamide copolymers,polyimides, polyesters (e.g., polyethylene terephthalates andpolybutylene terephthalate), polycarbonates, acrylonitrile butadienestyrene copolymers, polystyrenes, ethylene copolymers including at least80 wt. % ethylene, copolymers including any of these polymers, blends ofany of these polymers, or any combination thereof.

Preferable polyolefins include polypropylene homopolymers (e.g.,isotactic polypropylene homopolymer), polypropylene copolymers (e.g.,random polypropylene copolymers, impact polypropylene copolymer, orother polypropylene copolymer containing isotactic polypropylene),polyethylene homopolymer (e.g., high density polyethylene, or otherpolyethylene having a density greater than about 0.94 g/cm³),polyethylene copolymers (e.g., including at least about 80 wt. %ethylene), a blend of any of these polymers, or any combination thereof.Polypropylene homopolymers and polypropylene copolymers may besubstantially free of atactic polypropylene. If present, theconcentration of atactic polypropylene in the polypropylene preferablyis less than about 10 wt. %. Suitable polypropylene copolymers andpolyethylene copolymers include copolymers that consist essentially of(e.g., at least 98% by weight), or consist entirely of one or moreα-olefins. Other polypropylene copolymers and polyethylene copolymersthat may be used include copolymers containing one or more comonomersselected from the group consisting acrylates, vinyl acetate, acrylicacids, or any combination thereof. The concentration of the comonomermay be less than about 25 wt. %, preferably less than about 20 wt. %,and more preferably less than about 15 wt. % based on the total weightof the copolymer. Exemplary polyethylene copolymers that may be usedinclude ethylene-co-vinyl acetate (i.e., “EVA”, for example containingless than about 20 wt. % vinyl acetate), ethylene-co-methyl acrylate(i.e., EMA), ethylene co-methacrylic acid, or any combination thereof.

Suitable polyamides include reaction products of a diamine and a diacid,and monadic polyamides. Exemplary polyamides which are formed from adiamine and a diacid may include polyamides (e.g., nylons) containingreaction products of either adipic acid or terephthalic acid with adiamine. Exemplary monadic polyamides include nylon 6, andpoly(p-benzamide). Nylons which may be used in the present inventioninclude nylon 3, nylon 4, nylon 5, nylon 6, nylon 6T, nylon 66, nylon6/66, nylon 6/66/610, nylon 610, nylon 612, nylon 69, nylon 7, nylon 77,nylon 8, nylon 9, nylon 10, nylon 11, nylon 12, and nylon 91. Copolymerscontaining any of the above mentioned polyamides may also be used.Polyamide copolymers may include a polyether. Polyamide copolymers maybe random copolymers, block copolymers, a combination thereof.Polyethers which may be used with a polyamide copolymer may includeglycols. Exemplary glycols which may be used include propylene glycol,ethylene glycol, tetramethylene glycol, butylene glycol, or anycombination thereof. Polyamide copolymers may include a plurality ofpolyamides. An exemplary polyamide copolymer that includes a pluralityof polyamides is polyamide 6/66 which includes polyamide 6 and polyamide66. Suitable polyamide 6/66 copolymers may include less than about 50wt. % polyamide 66 based on the total weight of the polymer.

The thermoplastic polymers are preferably relatively long chainpolymers, such that they may have a number average molecular weightgreater than about 20,000, preferably greater than about 60,000, andmost preferably greater than about 140,000. They may be unplasticized,plasticized, elastomer modified, or free of elastomer. Semi-crystallinepolymers may have a degree of crystallinity greater than about 10 wt %,more preferably greater than about 20 wt %, more preferably greater thanabout 35 wt %, more preferably greater than about 45 wt %, and mostpreferably greater than about 55 wt %. Semi-crystalline polymers mayhave a degree of crystallinity less than about 90 wt %, preferably lessthan about 85 wt %, more preferably less than about 80 wt %, and mostpreferably less than about 68 wt %. Crystallinity of the thermoplasticpolymer may be measured using differential scanning calorimetry bymeasuring the heat of fusion and comparing it to art known heat offusion for the specific polymer.

The polymer of the filled polymeric material may also contain up toabout 10 wt % of a grafted polymer (e.g., a grafted polyolefin such asisotactic polypropylene homopolymer or copolymer) which is grafted witha polar molecule, such as maleic anhydride.

The thermoplastic polymer may include a substantially amorphous polymer(e.g., a polymer having a crystallinity less than about 10 wt. %,preferably less than about 5 wt. %, and most preferably less than about1 wt. %, as measured by differential scanning calorimetry at a rate ofabout 10° C./min). For example, the thermoplastic polymer may include asubstantially amorphous polymer having a glass transition temperaturegreater than 50° C., preferably greater than 120° C., more preferablygreater than about 160° C., even more preferably greater than about 180°C., and most preferably greater than about 205° C., as measured bydynamic mechanical analysis at a rate of about 1 Hz. Exemplary amorphouspolymers may include polystyrene containing polymers, polycarbonatecontaining polymers, acrylonitrile containing polymers, and combinationsthereof.

Examples of polystyrene containing polymers may include polystyrenehomopolymers, impact modified polystyrenes, polystyrene blockcopolymers, and polystyrene random copolymers. Polystyrene blockcopolymers which may be used include block copolymers containing one,two, three, or more polystyrene blocks, and one or more blocks selectedfrom the group consisting of butadiene, isoprene, acrylonitrile, or anycombination thereof. The polystyrene block copolymer may be unsaturated,partially saturated, or completely saturated (e.g., the block copolymermay include an unsaturated comonomer, which, after polymerization isfurther reacted to remove some or all of the double bonds). Exemplarystyrene block copolymers may include styrene-butadiene-styrene (SBS)block copolymers, acrylonitrile-butadiene-styrene (ABS) blockcopolymers, styrene-isoprene-styrene (SIS) block copolymers, andstyrene-acrylonitrile block copolymers (SAN). Blends of styrenecontaining polymers with other styrene containing copolymers, or withother amorphous polymers may also be used. For example, the polymer ofthe filled polymeric material may include a blend of a styrenecontaining polymer selected from the group consisting of ABS, SBS, SIS,SAN, and polystyrene homopolymer with a polycarbonate. A preferredamorphous copolymer is a blend of ABS and polycarbonate. Preferably, theABS and polycarbonate blend has an elongation at break greater thanabout 30%.

In lieu of or in addition to any thermoplastic polymer, the polymericlayer may employ an elastomer having one or both of the followingproperties: a relatively low tensile modulus at 100% elongation (e.g.,less than about 3 MPa, preferably less than about 2 MPa), a relativelyhigh tensile elongation at break (e.g., greater than about 110%,preferably greater than about 150%) both measured according to ASTMD638-08 at a nominal strain rate of about 0.1 s⁻¹. The elastomer mayfunction to improving the formability composite material, to increasethe ductility of the filled polymeric material, or both. The elastomermay be a synthetic elastomer, a natural elastomer, or a combinationthereof. Suitable elastomers may include styrene containing elastomer,ethylene containing elastomers, butadiene containing elastomers, naturalrubber, polyisoprene, butane containing elastomers, and acylonitrilecontaining elastomers. Suitable elastomers include block copolymers,random copolymers, and homopolymers. The elastomer may include polymermolecules that are functionalized with one or more functional groupsselected from maleic anhydride, a carboxylic acid, an amine, an alcohol,or an epoxide. A particularly preferred elastomer for rubber tougheningnylon is a functionalized EPDM, such as a maleic anhydride grafted EPDM.The elastomer may be cross-linked (e.g., cross-linked beyond the gelpoint of the elastomer) or substantially free of cross-links. Theelastomer may be substantially free of cross-links during a deformation(e.g., stamping) operation, and/or a welding (e.g., resistance welding)operation. The elastomer may include a curative, cure accelerator, orother chemical that will enable the elastomer to crosslink after adeformation operation (e.g., in a bake oven, such as an oven employedfor drying a coating on the panel). The elastomer preferably ischaracterized by a hardness of less than about 87 Shore A, morepreferably less than 70 Shore A, and most preferably less than about 50Shore A, as measured according to ASTM D2240.

Though it is possible that some amounts of epoxy may be used, thepolymer of the filled polymeric material preferably is substantiallyfree or entirely free of epoxy, or other brittle polymers (e.g.,polymers having an elongation at failure of less than about 20% asmeasured according to ASTM D638-08 at a nominal strain rate of about 0.1s⁻¹), or both. If present, the concentration of epoxy, other brittlepolymers, or both is preferably less than about 20%, more preferablyless than about 10%, more preferably less than about 5%, and mostpreferably less than about 2% by volume, based on the total volume ofthe filled polymeric material.

Polymers useful in the filled polymeric material may have a relativelyhigh coefficient of linear thermal expansion, e.g., above about 80×10⁻⁶.

Fillers

The filled polymeric material (e.g., the filled thermoplastic polymericlayer) contains one or more fillers. The fillers may be a reinforcingfiller, such as fibers, and more particularly metallic fibers. Fibersmay have an aspect ratio of the longest dimension to each perpendiculardimension (e.g., length to diameter) that is greater than about 10,preferably greater than about 20, and most preferably greater than about50. At least a portion of the fibers (e.g., the longitudinal directionof the metal fibers) may be preferentially oriented or they may berandomly dispersed in the filled polymeric material. For example, theoverall general longitudinal direction of at least some of the fibersmay be preferentially oriented perpendicular to the transverse directionof any layer of the filled polymeric material, or they may be randomlyoriented with respect to the transverse direction of any such layer. Themetallic fibers (e.g., the longitudinal direction of the metallicfibers) may be preferentially oriented in one, two, or more direction(s)within the plane of such layer, or they may be randomly oriented withinthe plane of the layer. The metallic fibers may be uniformly distributedwithin the filled polymeric material of any layer or they may beselectively located within the filled polymeric material of any layer.FIG. 2 illustrates an example of how fibers may be distributed. FIG. 2depicts a plurality of fibers oriented in a plurality of directions someof which are entangled with each other and which are attached topolymer.

The filled polymeric material may also contain one or more otherfillers, such as a filler particle (e.g., powders, beads, flakes,granules, and the like). As used herein, a filler particle is a fillerthat is not a fiber (i.e., it is not a filler having an aspect ratio ofthe longest direction to each perpendicular directions that is greaterthan about 10). The filler particle preferably has an aspect ratio ofthe longest direction to a perpendicular direction that is less thanabout 10, preferably less than about 8, and most preferably less thanabout 5. For example, the filled polymeric material may contain a fillerparticle selected from metallic particles, carbon, carbon black (e.g.,SRF, GPF, FEF, MAF, HAF, ISAF, SAF, FT and MT), surface-treated carbonblack, silica, activated calcium carbonate, light calcium carbonate,heavy calcium carbonate, talc, mica, calcium carbonate, magnesiumcarbonate, clay, calcium silicate, hydrotalcite, diatomaceous earth,graphite, pumice, ebonite powder, cotton flock, cork powder, bariumsulfate, wollastonite, zeolite, sericite, kaolin, pyrophyllite,bentonite, alumina silicate, alumina, silicon oxide, magnesium oxide,zirconium oxide, titanium oxide, iron oxide, iron phosphide, dolomite,calcium sulfate, barium sulfate, magnesium hydroxide, calcium hydroxideand aluminum hydroxide, boron nitride, silicon carbide, glass, and anycombination thereof. Exemplary fillers which may be used in the filledpolymeric material include metallic particles, carbon black, graphite,nano-clay particles, or any combination thereof. The concentration ofparticle fillers is preferably less than about 10 volume %, morepreferably less than 5 volume %, and most preferably less than 2 volume%, based on the total volume of the filled polymeric material. One ormore filler may include a nano tube structures, a layered structures, anintercalated structure, or some other structure.

Exemplary metallic fibers which may be used in the invention includefibers formed from metals such as steel (e.g., low carbon steel,stainless steel, and the like), aluminum, magnesium, titanium, copper,alloys containing at least 40 wt % copper, other alloys containing atleast 40 wt % iron, other alloys containing at least 40 wt % aluminum,other alloys containing at least 40 wt % titanium, and any combinationthereof. Any of the metals which may be used for the metallic layer(s),as described later, may also be used for the metallic fibers. Some orall of the metal fiber may be of a metal or a metal alloy that isgenerally corrosion resistant (e.g. stainless steel), or some or all ofthe metal fiber may be of a metal or metal alloy (e.g., aluminum,magnesium, or both) that offers cathodic protection to the metalliclayers and/or to other metallic fibers. The filled polymeric materialmay include metallic fibers that are of the same material or metallicfibers from a plurality of different materials. For example, some of themetallic fibers may be of a metal or metal alloy that offers cathodicprotection. Preferably, the concentration of the fibers of a metal ormetal alloy that offers cathodic protection is less than 60 wt. %, morepreferably less than 20 wt. %, and most preferably less than about 10wt. % based on the total weight of the metallic fiber. Mixtures ofdifferent metallic fibers may also be used.

The filled polymeric material may contain non-metallic conductivefibers, such as carbon fibers, fibers formed from conductive polymers,and the like. If present, the weight ratio of the non-metallic fibers tothe metallic fibers is preferably greater than about 1:10, morepreferably greater than about 1:5, and most preferably greater thanabout 1:3. If present, the weight ratio of the non-metallic fibers tothe metallic fibers is preferably less than about 10:1, more preferablyless than about 5:1, and most preferably less than about 3:1. It will beappreciated that filled polymeric material that are capable of beingwelded may also be prepared using non-metallic conductive fibers inplace of the metallic fibers. Conductive polymers which may be usedinclude polymers include poly(acetylene)s, poly(pyrrole)s,poly(thiophene)s, polyanilines, polythiophenes, poly(p-phenylenesulfide), poly(para-phenylene vinylene)s (i.e., PPV), polyindole,polypyrene, polycarbazole, polyazulene, polyazepine, poly(fluorene)s,and polynaphthalene, any blend thereof, any copolymer thereof, or anycombination thereof. PPV and its soluble derivatives have emerged as theprototypical electroluminescent semiconducting polymers. Exemplarythiophenes which may be used include poly(3-alkylthiophene)s (such aspoly(3-octylthiophene) and poly(3-(4-octylphenyl)thiophene)),poly(3-(alkylsulfanyl)thiophene)s, polybromothiophenes (such aspoly(2-bromo-3-alkylthiophene), poly(2,5-dibromothiophene), and thelike), polybithiophenes (such as poly(2,2′-bithiophene)s), or anycombination thereof.

The weight average length, L_(avg), of the metallic fibers may begreater than about 0.5 μm, preferably greater than about 5 μm, morepreferably greater than about 100 μm, even more preferably greater thanabout 1 mm, even more preferably greater than about 2 mm, and mostpreferably greater than about 4 mm. Suitable fibers may have a weightaverage length of less than about 200 mm, preferably less than about 100mm, more preferably less than about 55 mm, and most preferably less thanabout 25 mm. The metallic fibers may also be described by the dispersityof the lengths. For example the metallic fibers may have a relativelynarrow dispersity of lengths such that greater than 50% (or even greaterthan 70%) of the metallic fibers have a length between 0.8*L_(avg) and1.2* L_(avg). The metallic fibers may have a relatively broad dispersitysuch that less than 50% (or even less than 30%) of the metallic fibershave a length between 0.8*L_(avg) and 1.2* L_(avg). The metallic fibersmay also be characterized by the weight average diameter of the fibers.The weight average diameter of the fibers may be greater than about 0.01μm, preferably greater than about 0.1 μm, more preferably greater thanabout 0.5 μm, even more preferably greater than about 1.0 μm, even morepreferably greater than about 3 μm, and most preferably greater thanabout 12 μm. The weight average diameter of the fiber may be less thanabout 300 μm, preferably less than about 100 μm, more preferably lessthan about 50 μm, and most preferably less than about 30 μm.

The concentration of the metallic fibers is preferably greater thanabout 1 volume %, more preferably greater than about 3 volume %, evenmore preferably greater than about 5 volume %, even more preferablygreater than about 7 volume %, even more preferably greater than about10 volume %, and most preferably greater than about 12 volume % based onthe total volume of the filled polymeric material. The metallic fibersmay be present in the filled polymeric material at a concentration lessthan about 60 volume %, preferably less than about 50%, more preferablyless than about 35 volume %, still more preferably less than about 33volume %, and most preferably less than about 30 volume % (e.g., lessthan about 25 volume %, or even less than about 20, 10, or 5 volume %).For example the amount of fiber may be about 1%, 2%, 3%, 4%, 5%, 6%, 7%,8%, 9%, or 10%, by volume based on the total volume of the filledpolymeric material, or within a range bounded by those values (such asfrom about 1 % to about 6%). It is possible that composites herein mayemploy a concentration of metallic fibers that surprisingly issubstantially lower than the amount of a particle filler necessary toachieve similar welding characteristics. Moreover, it is also possiblethat the fibers and materials are selected so that better weldingperformance surprisingly may be realized at a relatively lowconcentration of metallic fibers as compared with an identical compositematerial having a higher concentration of metallic fibers. For example,it is surprisingly seen that using a filled polymeric material havingabout 10 volume % metallic fiber results in composite materials havingsuperior welding characteristics compared with those made with filledpolymeric materials having higher concentrations of metallic fiber.

The thermoplastic polymer material may be present in the filledpolymeric material at a concentration greater than about 40 volume %,preferably greater than about 65 volume %, more preferably greater thanabout 67 volume %, still more preferably greater than about 70 volume %,and most preferably greater than about 75 volume % (e.g., at least about80 volume %, at least about 90 volume %, or even at least about 95volume %).

The volume ratio of the polymer (e.g., the thermoplastic polymer) to thefibers (e.g., the metallic fibers) is preferably greater than about2.2:1, more preferably greater than about 2.5:1, and most preferablygreater than about 3:1. The volume ratio of the polymer (e.g., thethermoplastic polymer) to the fibers (e.g., the metallic fibers) ispreferably less than about 99:1, more preferably less than about 33:1,even more preferably less than about 19:1, and most preferably less thanabout 9:1, (e.g., less than about 7:1).

The material of any core in the sandwich composites herein may containpores or voids, or may be substantially free of pores and voids.Preferably, the concentration of pores and voids in the filled polymericmaterial is less than about 25 volume %, more preferably less than about10 volume %, still more preferably less than about 5 volume %, and mostpreferably less than about 2 volume % (e.g., less than about 1% byvolume), based on the total volume of the filled polymeric material.

The fiber (e.g., the conductive fiber, such as the metallic fiber)preferably is present at a concentration greater than about 40 volume %,more preferably greater than about 70 volume %, and most preferablygreater than about 80% (e.g., greater than about 90 volume %, or evengreater than about 95 volume %) based on the total volume of the fillerin the filled polymeric material.

The combined volume of the polymer (e.g., thermoplastic polymer) and themetallic fibers is preferably at least about 90% by volume, morepreferably at least about 95% by volume and most preferably at leastabout 98% by volume based on the total volume of the filled polymericmaterial.

The metallic fibers provide one or any combination of electricconductivity for welding, a reinforcement for strengthening, or strainhardening the polymeric structure by utilizing fibers that as metals arecapable of extending and imparting better strain hardening properties tothe polymeric core. As such, the tensile elongation (at failure) of themetal fibers is preferably greater than about 5%, more preferablygreater than about 30%, and most preferably greater than about 60% asmeasured according to ASTM A370-03a.

The metallic fibers, the metal particles, or both preferably reduces themelt flow rate of the filled polymeric material. The melt flow rate (asmeasured according to ASTM D1238, e.g., method K) of the filledpolymeric material is preferably at least about 20% less than, morepreferably at least about 40% less than, and most preferably at leastabout 60% less than the melt flow rate of the unfilled (i.e. the samepolymer as used in the filled polymeric material, but without themetallic fiber and other filler as taught).

It is possible that the materials herein may employ in combination withfibers, a metallic particle. Metallic particles may be spherical,elongated, or of any shape other than a fiber shape. Each metallicparticle may be characterized by a size equivalent to the diameter of aspherical particle having the same volume as the particle. Thus defined,the metallic particles may have an average size less than about 2 mm,preferably less than about 1 mm, more preferably less than about 0.1 mm,and most preferably less than about 0.07 mm (e.g., less than about 0.04mm).

The fibers (e.g., the metallic fibers) or the combination of the fibersand the metallic particles preferably are dispersed (e.g., randomlydispersed) in the polymeric matrix at a volumetric concentration of lessthan about 30% (more preferably less than about 25%, and most preferablyless than about 20%) by volume of the total polymeric layer). Ifmetallic particles are employed, the ratio of the volume of the fibers(e.g., the metallic fibers) to the volume of the metallic particles inthe filled polymeric material layer may be greater than about 1:30,preferably greater than about 1:1, and most preferably greater thanabout 2:1.

In one aspect of the invention, metallic particles, metallic fibers, orboth may be obtained by a step of grinding offal and/or scrap of astamping operation of a monolithic metal material or of a compositematerial (e.g. of a sandwiched plates, such as one made according to theteachings of the present invention), a machining operation or otheroperation that generates particles. This grinding operation may alsoproduce recycled polymeric material which may be melted together withthe thermoplastic polymer to produce the polymeric core. In such reclaimsteps, a substantial reduction in cost may be achieved.

In addition to the metallic fibers and the metallic particles, carbon inthe form of powder, graphite, grapheme, or any combination thereof, mayalso be added at a concentration preferably less than about 5 volume %based on the total volume of the polymeric layer, which may function,for example, to further increase the electric conductivity.

Nano-clay particles may also be used, which may function, for example,to improve the polymer ductility. When used, the concentration of thenano-clay particles preferably is less than about 5 volume % based onthe total volume of the polymeric layer.

Metal Layers

As discussed, it is envisioned that composites herein may employ asandwich structure by which a mass of a polymeric core is flanked onopposing sides by spaced apart layers. For example, a structure hereinmay include two sheets that have a metal fiber reinforced polymeric corematerial disposed between the sheets in contact with the sheets. Themetal layers (e.g., the first metallic layer and the second metal layer)of the sandwich construction may be made of a suitable material (e.g.,metal) in the form of foils or sheets or other layers having equal orunequal thickness (e.g., average thickness) across the layer. Eachmetallic layer may have a generally constant thickness or may have athickness that varies. The face metal on each side may be made ofmaterials having the same or different properties and be made of thesame or different metals. If the metal faces are made of metal sheets ofunequal thickness, materials having different properties, or materialshaving different metal. The composite material may have a marking orother means of identifying and distinguishing the different metal faces.The layers may be the same or different in composition, size (e.g.,thickness, width, volume, or otherwise), shape, or other features,relative to each other layer.

The metal layers may contain a pure metal or metal alloy containing atleast about 40 mole % of one of the following metals: Fe (iron), Ni(nickel), Al (aluminum), Cu (copper), V (vanadium), Cr (chromium), or Ti(titanium). The metal faces may contain an alloy comprising two or moremetals selected from the group consisting of Fe, Ni, Al, Cu, V, Ti, Cr,Mo (molybdenum), Mn (manganese), Mg (magnesium), or W (tungsten). Suchmetals or metal alloys may also contain additional metals or non-metals.For example, suitable metals for the face metal may also contain C(carbon), or Si (silicon) at a concentration less than about 10 mole %.Exemplary materials which may be used for the metallic faces includeregular steel, high strength steel, medium strength steel,ultra-high-strength steel, stainless steel, titanium, aluminum and theiralloys. The metal or metal alloy may have one or more crystallinephases. For example, the metal alloy (as may any fiber used) may have acrystalline phase selected from the group consisting of hexagonal closedpack, face center cubic, simple cubic, and body center cubic. Themetallic layer may contain ferritic steel, austenitic steel, cementite,or any combination thereof. The metallic layer may be annealed, coldhardened, heat treated, precipitation hardened, or otherwise treated.The metallic layer may have relatively large grain size (e.g., greaterthan about 3 mm), or relatively small grain size (e.g., less 3 mm). Themetal faces may have one or more surfaces plated or coated with a thinfilm. Exemplary coatings and platings may include one or any combinationof galvanized, electrogalvanized, chrome plating, nickel plating,corrosion resistance treatment, e-coat, zinc coated, Granocoat, Bonazincand the like. Preferably, one or both of the metal faces are free of acoating with a material having an electrical resistivity less than about10 Ω·cm. A combination of different metallic materials may be used byhaving different kinds of metal faces on opposing sides of the polymericlayer and/or by using tailored blanks that combine different alloys(e.g., different grades of steel) and thicknesses of metals into asingle blank. For a laminate containing only one metal face, the abovementioned metals may be used for the metal face (i.e. for the firstmetallic layer).

One or both of the metal faces preferably may be relatively thick, suchthat the metal face does not wrinkle, tear, or form other defects whenpreparing and/or processing the composite material. Preferably, thethickness of one or both of the metal faces is at least about 0.05 mm,more preferably at least about 0.10 mm, even more preferably at leastabout 0.15 mm, and most preferably at least about 0.18 mm. The sheetsmay have a thickness less than about 3 mm, preferably less than about1.5 mm, and more preferably less than about 1 mm, and most preferablyless than about 0.5 mm. For example, the composite material may be usedin an automotive panel requiring at least one class A or class Bsurface, preferably at least one class A surface. Such a compositematerial may have a first surface which is a class A surface and asecond surface which is not a class A surface. The class A surface mayhave a first metal face having a relatively high thickness and a secondsurface that has a second metal face having a relatively low thickness(e.g., at least about 20% or even at least about 40% less than thethickness of the first metal face). In general, the ratio of thethickness (e.g., average thickness) of the first metal layer to thethickness of the second metal layer may be from about 0.2 to about 5,preferably from about 0.5 to about 2.0, more preferably from about 0.75to about 1.33 and most preferably from about 0.91 to about 1.1.

Composite Material

The composite material may be in the form of a multi-layered sheet,e.g., a sandwich structure including sheets of a material such as ametal that sandwich a core of the filled polymeric material. The sheetsmay have a total average thickness less than about 30 mm, preferablyless than about 10 mm, more preferably less than about 4 mm and mostpreferably less than about about 2 mm; and preferably greater than about0.1 mm, more preferably greater than about 0.3 mm, and most preferablygreater than about 0.7 mm). The composite material may have a generallyuniform thickness or the composite material may have a thickness thatvaries (e.g., a random or periodic variation in one or more directions).For example, the variation in the thickness may be such that thestandard deviation of the thickness is less than about 10% of theaverage thickness. The standard deviation of the thickness is preferablyless than about 5% of the average thickness, more preferably less thanabout 2% of the average thickness, and most preferably less than about1% of the average thickness.

The thickness of the filled polymeric layer may be greater than about10%, 20% 30%, 40%, or more of the total thickness of the compositematerial. The volume of the filled polymeric layer may be greater thanabout 10%, 20%, 30%, 40%, or more of the total volume of the compositematerial. Preferably, greater than 50% of the volume of the compositematerial will be the filled polymeric material. The concentration of thefilled polymeric material is more preferably greater than about 60volume % and more preferably greater than about 70 volume % based on thetotal volume of the composite material. The concentration of the filledpolymeric material is typically less than 92 volume % based on the totalvolume of the composite material; however, higher concentrations may beused, particularly in relatively thick composites (e.g., having athickness greater than about 1.5 mm).

The total thickness of outer layers of a sandwich composite structureherein (e.g., metallic layers) may be less than about 70% of the totalthickness of the composite material. The total thickness of metalliclayers preferably is less than about 50%, more preferably less thanabout 40% and most preferably less than about 30% of the total thicknessof the composite material. The total thickness of the outer layers(e.g., the metallic layers) may be greater than about 5%, preferablygreater than about 10%, and more preferably greater than about 20% ofthe total thickness of thickness of the composite material.

The polymeric core layer preferably is in contact (direct or indirect,such as via a primer and/or adhesive layer) with at least a portion ofthe surface of the adjoining layers (e.g., one or more metallic layer)facing the core layer. Preferably, the area of contact is at least about30%, more preferably at least about 50%, most preferably at least about70% of the total area of the surface of the adjoining layer facing thepolymeric core layer.

The composite material may include a plurality of polymeric core layers.For example, the composite material may include one or more core layerswhich includes an adhesive such that it adheres to a metallic layer, adifferent core layer, or both.

The composite material may have a relatively high stiffness (e.g.,flexural stiffness (i.e., apparent bending modulus) as measured at about20° C. according to ASTM D747) to density ratio. For example, thecomposite material containing at least 30 volume % of core material andhaving a thickness, t, may have a stiffness to density ratio which isgreater than the stiffness to density ratio of a sheet made of the samematerial (e.g., metal) as the face material (e.g., metals), and havingthe same thickness t. The stiffness to density ratio of the compositematerial may exceed the stiffness to density ratio of a sheet of theface material (e.g., metal) having the same thickness by greater thanabout 5%, preferably greater than about 10%, more preferably greaterthan about 14%, and most preferably greater than about 18%.

The layers adjoining the filled polymeric material (e.g., metalliclayers) typically have a relatively low coefficient of linear thermalexpansion. For example, the ratio of the coefficients of linear thermalexpansion of a metallic layer to the thermoplastic polymer may be fromabout 1:30 to about 1:3, more preferably from about 1:15 to about 1:5.The composite material surprisingly does not delaminate or otherwisefail after cycling between extreme ambient temperatures (e.g., between−40° C. and +40° C.) despite the large difference in the coefficients oflinear thermal expansion between the polymer phase and the adjoiningmaterials (e.g., the metallic face material). Without being bound bytheory, it is believed that the relatively low coefficient of thermalexpansion of the metallic fibers reduces the coefficient of linearthermal expansion of the filled polymeric material so that delaminationis reduced or even eliminated.

Process for Preparing the Composite

The composite material may be prepared using a process that results inthe filled polymeric material (e.g., core layer) being bonded to atleast one adjoining layer (e.g., a metallic sheet) and preferably beinginterposed between two layers (e.g., two metallic layers) and bonded toone or both layers. The process may include one or any combination ofsteps of heating, cooling, deforming (e.g., forming, such as bystamping), or bonding, in order to arrive at a final desired article. Itis envisioned that at least one, or even all of the adjoining layers(e.g., metallic layers) may be provided in the form of a rolled sheet, aforging, a casting, a formed structure, an extruded layer, a sinteredlayer, or any combination thereof.

The sheets may be heated to a temperature greater than about 90° C.(e.g. greater than about 130° C., or greater than about 180° C.).Preferably, the sheets are heated to a temperature greater than aboutT_(min), where T_(min) is the highest glass transition temperature(T_(g)) and melting temperature (T_(m)) of the filled polymericmaterial. The metallic sheets, the filled polymeric material, or bothmay be heated to a maximum temperature above which the polymer (e.g.,the thermoplastic polymer) may undergo significant degradation. Thethermoplastic polymer may be heated to a temperature preferably lessthan about 350° C., more preferably less than about 300° C. The heatedpolymer may be mixed with the metallic fiber, and with any additionalfillers. The heated polymer (e.g., thermoplastic polymer) may beextruded as a sheet layer. The sheet layer may be extruded directlybetween the metal faces, or placed between the metal faces later in theprocess or in a separate step.

The polymeric core layer may be a homogeneous layer or may comprise aplurality of sublayers. For example, the filled polymeric material maycontain an adhesive layer (e.g. on one or more surfaces). If employed,the adhesive layer or layers preferably include metallic fibers,conductive filler particles (e.g., a conductive filler particle selectedfrom the group consisting of metallic particles, carbon black, graphite,iron phosphide, and combinations thereof), or both. Such an adhesivelayer may be selected and applied to provide sufficiently good adhesion(e.g., a cohesive failure mode is observed when peeling the metal layerfrom the polymeric layer) to the metal face, the polymeric core, orboth. It is also contemplated that some of the fibers from the polymericcore may protrude or penetrate into the adhesive (e.g., into theadhesive layer). An adhesive layer may include a conductive fiber (e.g.,the adhesive layer may be a fiber-filled polymeric layer that includesmetallic fiber). The composite material may be free of any adhesiveand/or adhesive layer.

The process for fabricating the composite material may also include oneor more steps of heating one or more metal layers, applying pressure tothe layers, calendaring a polymer (e.g., a thermoplastic polymer or thethermoplastic polymer compounded with the metallic fiber and theoptional fillers), and annealing the composite sheet (e.g., at atemperature greater than the melting temperature of any thermoplasticpolymer in the material).

The process for preparing the filled polymeric material (e.g., a corelayer for the sandwich composites herein) may include a step ofcontacting the fiber and the polymer (e.g., thermoplastic polymer). Thestep of contacting the fiber and the polymer may occur prior to, orduring a step of forming the filled polymeric material. For example, aprecursor feedstock filled polymeric material including the fiber and atleast a portion of the polymer may be prepared by a pultrusion processincluding a step of pultruding a single fiber or preferably a pluralityof fibers through a polymer in a liquid state (e.g., a moltenthermoplastic polymer), such that the fibers are coated with thepolymer. The process of preparing a precursor feedstock polymer materialpreferably employs continuous fibers and the feedstock material ispreferably chopped into pellets, granules, rods, or other shape (eachtypically having a mass of less than about 2 grams) suitable for feedinginto a polymer extruder or other polymer processing equipment. As such,the fibers in each pellet, granule, or rod, will aligned in a generallyaxially orientation. As another example, a precursor feedstock filledpolymeric material may be prepared by blending the fibers and at least aportion of the polymer (e.g., the thermoplastic polymer) in an extruder,internal mixer, mill, or other polymer mixing equipment, at atemperature at which the polymer flows. In another approach, the fiberand the polymer are contacted during the process of preparing thepolymeric layer. For example, fiber and polymer (e.g., thermoplasticpolymer) materials may be dry blended and fed into a polymer processingequipment, they may be fed individually but at the same time andlocation into the polymer processing equipment, or they may be fed intodifferent locations or at different times into the polymer processingequipment. The process of forming a precursor feedstock filled polymericmaterial or of forming the polymeric layer may include a step ofchopping the fibers and feeding them directly into the polymerprocessing equipment (such a process may be free of a step of storingthe chopped fibers, or include a step of contacting the fibers with apartitioning agent (e.g., a powder such as a powder filler or a powderpolymer)). The process of forming the polymeric layer may be acontinuous process or a batch process. Preferably, the process is acontinuous process.

The process may include a step of providing a third metal layer (inaddition to the first and second metal layer). It may include a step ofinterposing a second polymeric core layer between the second metal layerand the third metal layer, such that the second metal layer isinterposed between the two polymeric layers. When employed, the thirdmetallic layer preferably may be perforated (e.g., having a plurality ofopenings covering at least about 20%, more preferably at least about40%, and most preferably at least about 60% of the surface of the thirdmetallic layer).

The process may include a step of contacting a filled polymeric materialsurface of a laminate with the surface of either a second metallic layeror a filled polymeric material of a second laminate at a temperaturegreater than T_(min), where T_(min) is the greater of the highestmelting temperature or the highest glass transition temperature ofpolymer in the filled polymeric material, such that the contactingsurfaces at least partially bond and forms a composite having a filledpolymeric material layer interposed between two metallic layers. Theprocess may also contain a step of applying pressure to the first andsecond metal layer, e.g., by feeding the composite material through oneor more pairs of rollers having a predetermined spacing. The step ofapplying pressure preferably occurs when at least some of the polymer ofthe filled polymeric material (e.g., the thermoplastic in contact withthe metal layer) is above T_(min). For example, the step of applyingpressure may occur when at least some of the polymer of the filledpolymeric material is at a temperature greater than about 80° C.,preferably greater than about 120° C., more preferably greater thanabout 180° C., even more preferably greater than about 210° C., and mostpreferably greater than about 230° C. The process may also include astep of cooling the composite material (e.g. to a temperature belowT_(min), preferably below the melting temperature of polymer of thefilled polymeric material, and more preferably below about 50° C.).

The process may also include a step of applying one or more spacers forseparating opposing layers and in the space into which the filledpolymeric material is introduced (e.g., between first and second metallayers). Structures herein thus also contemplate inclusion of one ormore spacers between the layers. For example, a spacer may be entirelyinterposed between two opposing layers, or the spacer may have a firstsection that is interposed between two opposing layers and a secondsection (which may have a larger thickness than the first section) thatis not interposed between the layers. The spacer may be a rod, a bead, amember having a profile (e.g., a profile having a generally uniformcross-section), a deformation deliberately formed into a metal layer, orany combination thereof.

The composite material may be a laminate, which preferably has a uniformthickness. The variation in the thickness of the laminate may be thesame as for the sheet as described above. The process for manufacturingthe laminate may be similar to the process for manufacturing the sheet,except that only one metal sheet is utilized.

It may be preferable for the process for manufacturing the compositematerial to be free of a step of heating the composite material to atemperature at which the metallic fibers may sinter or otherwise fusedirectly together (e.g., in a metallurgical bond), to a temperature atwhich the metallic fibers undergo a phase transition, to a temperatureat which internal stresses in the metallic fibers are relieved (e.g.,following an operation of stamping the composite), or any combinationthereof.

In lieu of, or in addition to fibers, the process of preparing the acore filled polymeric material layer may employ a printing (e.g., aninkjet printing) or lithography (e.g., photolithography) process todeposit a plurality of layers including metal to build a 3-dimensionalelectrically conductive metallic network. Such a metallic network may bepresent in any of the concentration ranges described herein for thefibers.

In yet another approach, the filled polymeric layer may be formed bycontacting the fibers with one or more monomers or prepolymers, followedby a step of polymerizing the one or more monomers or prepolymers. Thepolymerization may occur in a processing equipment (e.g., in anextruder), on a form, or in a mold; on a metallic layer, between twometallic layers, or the like.

The teachings herein generally contemplate sandwich structures that areopen at their edges. However, the process may include a step of treatingthe edge of the composite material to seal the edge. One or more edgesof the composite material may be sealed by a mechanical operation (e.g.,crimping or bending of the composite material), by a cover (e.g., acoating, a lamination, or an attached cover), or by a welding,soldering, or brazing operation.

Forming Process

The composite material of the present invention may be subjected to asuitable forming process, such as a process that plastically deforms amaterial and may include a step of stamping, roll forming, bending,forging, punching, stretching, coiling, some other metalworking, or anycombination thereof. A preferred forming process is a process thatincludes a step of stamping the composite material. The stamping processmay occur at or near ambient temperatures. For example, the temperatureof the composite material during stamping may be less than about 65° C.,preferably less than about 45° C., and more preferably less than about38° C. The forming process may involve drawing regions of the compositematerial to various draw ratios. In one aspect of the invention, thecomposite material is subjected to a step of drawing to a relativelyhigh draw ratio without breaking, wrinkling, or buckling. For example,it is subjected to a step of drawing so that at least a portion of thecomposite is drawn to a draw ratio greater than 1.2. Desirably, thecomposite material may be capable of being drawn and is drawn to amaximum draw ratio greater than about 1.5, preferably greater than about1.7, more preferably greater than about 2.1, and most preferably greaterthan about 2.5. The cracking limit of the draw ratio may be determinedusing the circular cup drawing test as described by Weiss et al. (M.Weiss, M. E. Dingle, B. F. Rolfe, and P. D. Hodgson, “The Influence ofTemperature on the Forming Behavior of Metal/Polymer Laminates in SheetMetal Forming”, Journal of Engineering Materials and Technology, October2007, Volume 129, Issue 4, pp. 534-535), incorporated herein byreference. The forming process may include a step applying a pressure toa die (e.g., a die having a hardness, as measured according to Mohrshardness scale, greater than the hardness of the metallic fibers) incontact with the composite material.

During a stamping or drawing process, composites including a porousmetallic fiber core (i.e., a core that is substantially free ofthermoplastic and optionally including an adhesive layer) interposedbetween two metallic layers; the fibers tear and/or the two metalliclayers delaminate, unless the concentration of fibers is high or thefiber is replaced with perforated metal containing at least about 28%metal by volume, as demonstrated by Mohr (Dirk Mohr, “On the Role ofShear Strength in Sandwich Sheet Deforming,” International Journal ofSolids and Structures, 42 (2005) 1491-1512). In the present invention,the failure mechanisms observed by Mohr are surprisingly overcome byemploying a polymeric core layer having relatively low concentrations ofmetallic fiber (e.g., including less than about 28% metallic fiber basedon the total volume of the core). Without being bound by theory, it isbelieved that the improved deformation characteristics at low metallicfiber concentration is related to the core layer being substantially oreven completely free of pores and/or voids. The composite structuresillustrated herein have an unexpectedly high amount of deformation(e.g., a relatively high draw ratio) prior to fiber tearing and/ordelamination of the metallic layers.

A particularly preferred stamping or drawing process is a process thatoperates at greater than about 1 stroke (e.g., 1 part) per minute, morepreferably greater than about 5 strokes per minute, even more preferablygreater than about 25 strokes per minute, and most preferably greaterthan about 60 strokes per minute. The stamping process may include ablank holding force to hold a periphery of the blank (i.e., a peripheryof the composite material being stamped). Preferably, the blank holdingforce is greater than about 0.03 kg/mm², more preferably greater thanabout 0.10 kg/mm², and most preferably greater than about 0.18 kg/mm².The stamping process may include one, two, or more drawing steps.Preferably, the maximum draw for the first draw of the stamping process(as measured by the maximum % reduction in thickness) is less than about60%, more preferably less than about 50% and most preferably less thanabout 45%. In addition to drawing the material, the stamping process mayinclude one or more steps of piercing the part, trimming the part,flanging the part, or any combination thereof, which may be a separatestep or may be combined (e.g., with a drawing step).

Characteristics of Composites

The composite material, when tested according to the channel bendingmethod (e.g., at 23° C.) described by Weiss et al. (M. Weiss, M. E.Dingle, B. F. Rolfe, and P. D. Hodgson, “The Influence of Temperature onthe Forming Behavior of Metal/Polymer Laminates in Sheet Metal Forming,”Journal of Engineering Materials and Technology, October 2007, Volume129, Issue 4, pp. 530-537) may have a wall springback angle less thanabout 10%, preferably less than about 8%, more preferably less thanabout 5%, and most preferably less than about 2%. When tested by thesame method, the composite material may be characterized by a flangespringback angle less than about 2%, preferably less than about 1.5%,and more preferably less than about 1.0%.

Preferably, the composite material is weldable (e.g., weldable using aresistance welding technique such as spot welding, seam welding, flashwelding, projection welding, or upset welding) and has a relatively lowelectrical resistance. The teachings herein thus also contemplate one ormore steps of welding the composite materials taught herein. Theelectrical resistance of the composite material in the through-directionmay be described by the sum of the electrical resistance of the metalliclayers and the core layer. Typically, the electrical resistance of themetallic layers is much less than the electrical resistance of the corelayer, such that the electrical resistance of the composite material maybe estimated by the electrical resistance of the core layer. Theresistivity (e.g., the resistivity measured in the through-thicknessdirection, normal to the plane of a sheet) may be measured using ACmodulation and determined from the voltage drop, V, and the current, I:

Resistivity=(V/I) (A/t)

where A is the area of the sheet, and t is the thickness of the sheet.The resistivity (in the through-thickness direction) of the compositematerial, the core layer, or both, may be relatively low (e.g., thecomposite material, the core layer, or both, may be characterized by aresistivity less than about 100,000 Ω·cm, preferably less than about10,000 Ω·cm, more preferably less than about 3,000 Ω·cm, and mostpreferably less than about 1,000 Ω·cm).

The composite materials of the present invention may provide forimproved thermal characteristics compared with a monolithic metallicmaterial having the same dimensions. Preferably, the composite materialmay have a relatively low thermal conductivity (e.g., the compositematerial may be a sheet having a relatively low thermal conductivitymeasured in the through-thickness direction, normal to the plane of thesheet). For example, a composite material according to the teachingsherein may have a thermal conductivity (e.g., in the through-thicknessdirection) that may be less than (preferably at least about 10% lessthan, more preferably at least about 50% less than, and most preferablyis at least about 90% less than the thermal conductivity of a monolithicmaterial having the same dimensions as the composite material andconsisting of the same metal as used in a metallic layer of thecomposite. The thermal conductivity in the through-thickness directionof the composite material (measured at about 25° C.) preferably is lessthan about 25 W/m·°K, more preferably less than about 14 W/m·°K., evenmore preferably less than about 10 W/m·°K, even more preferably lessthan about 5 W/m·°K, and most preferably less than about 1 W/m·°K.

The composite material according to the teachings herein, may include acore layer that reduces acoustical transmission, reduces soundgeneration, reduces vibrations, or any combination thereof. The peakacoustical transmission (e.g., as measured according to SAE J1400), thepeak vibration transmission, or both, through the composite materialpreferably may be less than the value for a monolithic material havingthe same dimensions, more preferably by at least 10%, even morepreferably by at least 50%, and most preferably by at least 90%.

Microstructure of Weld

It is possible that weld joints made using various composites taughtherein may exhibit a variation of microstructures across the composite.For example, a joint might be characterized as having (on sideslaterally flanking the weld) spaced apart metal where each sheetincludes ferrite and optionally cementite (e.g., in a pearlitestructure). The weld itself may be characterized as including ferrite,carbide, and optionally austenite (e.g., in a banite structure).Progressing along the material length, there may be an increase in thecarbon content from the lateral locations of the weld joints.

Referring to FIG. 3A, a weld joint 30 may be formed between thecomposite material 12 (including a first metallic layer 14, a secondmetallic layer 14′ and a polymeric core layer 16) and a second metallicmaterial 36 (e.g., a second composite material or a monolithic metalmaterial, such as a steel sheet). The weld joint will have at least twoweld zones including a first weld zone 32 resulting from the welding ofthe first metallic layer 14 and the second metallic layer 14′ and asecond weld zone 34 resulting from the welding of the second metalliclayer 14′ and the second metallic material 36. The weld joint may alsoinclude a metal rich region 38 between the two metallic layers of thecomposite material and adjacent to the weld joint. The metal rich regionmay include metal that is squeezed out by the weld tips during a weldingoperation. For example, the metal rich region may include or consistessentially of metal from the metallic fibers in the composite. Withoutbeing bound by theory, it is believed that a welding operation may firstmelt the polymer under the weld tips and the weld pressure may forcesome or all of the polymer away from the weld (e.g., prior to melting ofthe metal), that a welding operation may melt some or all of themetallic fibers under the weld tips prior to melting the metalliclayers, or both. The concentration of carbon in the metal (and thus thehardness) at various regions of the first metallic layer as shown inFIG. 3A (32, 40, 41, 42) may be the same or different, and preferablyare the same. The microstructure of the first metallic layer near theweld zone 32, may be the same or different from the microstructure ofthe first metallic layer away from the weld zone 40. Differences inmicrostructure may result from different concentration of iron, carbon,other metals, or any combination thereof (such as may arise from mixingof the first metallic layer with atoms from the second metallic layer,the metallic fibers, the polymer, or any combination thereof), or fromdifferences in thermal treatment (such as from the heating and coolingcycle of the weld).

According to the teachings herein, the microstructure of the metal atthe weld zone 32 may have the same microstructure (e.g., the same carbonconcentration, the same crystal structures, such as a bainite structure,a pearlite structure, a pure ferrite structure, a martensite structure,an austenite structure, and the like, or any combination thereof) asobtained when welding the first metallic layer and the second metalliclayer without a polymeric layer. As such it is surprisingly found thatthe polymeric layer, including both a thermoplastic and metallic fibers,may not affect the microstructure of the weld joint.

The process may include one or more steps subsequent to a welding stepof treating the workpiece (i.e., the welded structure) such that amicrostructure is changed. For example, the workpiece may be annealed,mechanically worked, or treated by a surface hardness modification step(e.g., a carborization of the surface). A step where a microstructure ischanged may also be characterized as a step in which a phase transitionoccurs.

FIG. 3B illustrates the microstructure in the region near a weld joint30′. As illustrated in FIG. 3B, the polymeric layer 16 near the weldzone 32 may have varying concentrations of metallic fibers 20 andpolymer 18 moving laterally from the weld zone. For example, the weldzone may be partially or even entirely encircled by a metal ring 38, andhave one or more metallic fiber rich regions 39 (e.g., that may beformed when polymer is melted and squeezed out of the weld zone and outof regions near the weld zone). The thickness of the metallic layers 14and 14′ may have relatively little variation moving laterally away fromthe weld zone compared with the thickness of the polymeric layer whichmay have a relatively large variation. As illustrated in FIG. 3B, thethickness of the polymeric layer may be substantially reduced in theregion 39 adjacent to the weld joint compared with the thickness of thepolymeric layer prior to welding. For example the thickness of thepolymeric layer in the region adjacent to the weld joint may be reducedby at least 20%, preferably reduced by at least about 50%, and morepreferably reduced by at least about 60% compared to the thickness ofthe polymeric layer prior to any welding operation.

As discussed above and illustrated in FIG. 3B, the weld joint mayinclude a ring 38 of a metal partially encircling or entirely encirclingthe weld joint and preferably attached to the weld zone 32 of the weldjoint. The ring may have any cross-section, such as a triangle, arectangle, a trapezoid, a circle sector, and the like. As illustrated inFIG. 3B, the ring may have a cross-section that has a generally circlesector shape. Without being bound by theory, it is believed that thering is formed at least partially or even substantially entirely fromthe metallic fiber material (e.g., metallic fibers that are melted andsqueezed out during the welding operation), and may be of a differentmetal than the metals on either side of the weld zone 32 (i.e.,different metals from the first metallic layer and the second metalliclayer). As such the weld joint may include a first metallic layer havinga first metal in welded contact with a second metal of a second metalliclayer, wherein the first metal and the second metal are the same ordifferent; and a metallic ring at least partially encircling the weldzone (e.g., the weld zone defined by the region of contact of the firstand second metallic layers), disposed between the first and secondmetallic layers, and attached to the first, second, or both metalliclayers in the weld joint, wherein the metallic ring is of a metal thatis different from the first metal and the second metal.

The composite materials of the present invention may be used in anynumber of applications requiring one or any combination of theproperties described herein, including but not limited to relatively lowdensity, relatively low thermal conductivity, relatively high stiffnessto density ratio, or relatively low acoustical transmission. Exemplaryapplications which may employ the composite materials of the presentinvention may include automotive and other transportation relatedapplications, building construction related applications, and appliancerelated applications. The composite materials may be used inapplications such as an automotive panel, a truck panel, a bus panel, acontainer (e.g., a container used for shipping), a panel on a train car,a panel on a jet, a tube (e.g., a bicycle tube), a motorcycle panel, atrailer panel, a panel on a recreational vehicle, a panel on asnowmobile, an automotive bumper fascia, a spoiler, a wheel well liner,an aerodynamic ground effect, an air dam, a container, a bed liner, adivider wall, an appliance housing, or a seat pan. The compositematerials may be used as a building construction material, such as anexterior trim element, flashing, gutters, shingles, walls, flooring,countertops, cabinet facing, window frames, door frames, paneling,vents, ducts, planking, framing studies, shelving, plumbing fixtures,sinks, shower pans, tubs, and enclosures. An exemplary application is anvehicle body panel (e.g., a body outer skin of a vehicle such as anautomobile). Automobile panels which may use the composite materialsdescribed herein include front quarter panels, rear quarter panels, doorpanels, hood panels, roof panels, or otherwise. The automotive panel mayhave a class A, class B, or class C surface, preferably a class A orclass B surface, and more preferably a class A surface. The compositematerials herein may also include one or more decorative outer surfacesor veneers, such as a metal veneer, a wood veneer, a polymeric veneer,or otherwise. The outer surface may have a different texture, color orother appearance as an opposing layer. For example, a ferrous outerlayer may be colored so that it simulates a copper color, a bronzecolor, a brass color, a gold color, or some other color.

The composite materials of the present invention may be used in aprocess that includes a step of coating the composite material, such asan electrocoating process, a paint process, a powder coat process, anycombination thereof, or the like. If employed, the coating process mayinclude one or more steps of cleaning or otherwise preparing thesurface, one or more steps of heating or baking the coating (e.g., at atemperature greater than about 100° C., preferably greater than about120° C.), or any combination thereof. The coating may be applied by anyconventional means, such as by a dipping process, a spraying process, orwith a process employing an applicator such as a roller or a brush. Assuch, the composite material preferably is free of ingredients (e.g.,low molecular weight ingredients) that leach out and contaminate a bathof a coating process, such as a bath of an electrocoat process.Likewise, methods herein include one or more coating steps that are freeof bath contamination due to an ingredient of the composite.

The composite material (e.g., a stamped part formed of the compositematerial) may be used in an assembly which requires joining thecomposite material to one or more other materials or parts. For examplethe composite material may be mechanically joined to another part usinga fastener, or chemically joined to another part using an adhesive, anadhesion promoter (e.g., a primer), or both. Other means of joininginclude welding, brazing, and soldering. One or any combination of thesejoining methods may be employed.

Preferably, the composite material does not delaminate (e.g., themetallic layer does not delaminate from the core layer) during theprocessing of the composite material to form a part or an assembly. Assuch, the composite material preferably does not delaminate during astamping operation, during a joining operation (e.g., during a weldingoperation), or both. The composite material may be substantially free ofgas pockets where gas at an elevated pressure has accumulated betweenlayers. One or more layers may include one or more apertures to vent anyaccumulated gas. For example, a plurality of perforations in a metallayer may surround a weld site, and allow any gas to escape that mayarise due to welding. It is also possible that the polymeric layerincludes one or more cells into which gas may migrate to avoid pressurebuild up. Similar results are expected by use of plain carbon steel orother steel fibers.

Properties discussed herein may be exhibited over an entire part madeusing the composite materials herein, or over only a portion of it.Parts may be characterized as exhibiting substantially no visibledetectable read through of any fibers (i.e. an outer show surface isfree of visibly detectable (e.g., by the naked eye)) surfacedeformations that would be the result of compression of the layers withfibers between them. It is possible that, prior to any welding, themicrostructure of the metals may be substantially continuous across atleast a portion if not the entirety of the part.

It may be possible to selectively induce property differences atpredetermined locations across a part.

Another aspect of the invention contemplates a method for post-consumerreclamation, recycling, or both of parts made using the presentinvention. One approach envisions providing a part having the compositestructure taught herein, and subjecting it to a step of separatinghydrocarbon compounds (e.g., by an elevated temperature heating step)from the metallic materials. Either or both of the hydrocarbon compoundsor the metallic materials can be recovered and re-used.

It should be appreciated that the compositions of the following examplesmay be varied by about ±20% and give similar results (e.g., within about±20%). Further, other materials taught herein may be substituted forthose stated and similar results are contemplated.

EXAMPLES Example 1

The core material for the light weight composite is prepared by meltblending about 45 g nylon 6 and about 72 g stainless steel fibers havingan average diameter of about 3-10 μm and an average length of about 2-4mm in a Brabender Plastograph mixer at 260° C., with a speed of about 20rpm. The nylon 6 has a density of about 1.142 g/cm³ and the steel has adensity of about 7.9 g/cm³. After mixing for about 60 minutes, theadmixture is removed from the Brabender mixer. Thus prepared, example 1contains about 18.8 volume % steel fibers and about 81.2 volume % nylon6 and has a density of about 2.411 g/cm³.

Example 2

A core material is prepared using the same method as for Example 1,except the weight of the stainless steel fiber is about 102 g and theweight of the nylon 6 is about 40 g. Thus prepared, the admixturecontains about 26.9 volume % steel fibers and about 73.1 volume % nylon6 and has a density of about 2.962 g/cm³.

Example 3

A core material is prepared using the same method as for Example 1,except the weight of the stainless steel fiber is about 48 g and theweight of the nylon 6 is about 53.5g. Thus prepared, the admixturecontains about 15 volume % steel fibers and about 85 volume % nylon 6and has a density of about 2.157 g/cm³.

Example 4

A core material is prepared using the same method as for Example 1,except the weight of the stainless steel fiber is about 35.4 g and theweight of the nylon 6 is about 50.6 g. Thus prepared, the admixturecontains about 10 volume % steel fibers and about 90 volume % nylon 12and has a density of about 1.816 g/cm³.

Comparative Example 5

A core material is prepared using the same method as for Example 1,except no stainless steel fiber is used and about 53 g of the nylon 6 ismixed in the Brabender Plastograph mixer. Comparative Example 5 has adensity of about 1.142 g/cm³.

Comparative Examples 6-7

Composite materials are prepared by compression molding a sandwich panelcontaining two steel plates, each having a thickness of about 0.20 mm alength of about 74.2 mm and a width of about 124.2 mm, and the Nylon 12,without metallic fibers, is placed between the metal plates. The steelplates are made of No. 5 temper Aluminum killed) low carbon steel thatmeets AISA 1008 and ASTM A109 standards. The thickness of the corematerial for comparative examples 6 and 7 is about 0.30 mm, and about0.44 mm, respectively, as shown in Table 1. Comparative Example 6 and 7are compression molded using a positive mold at a temperature of about250° C. and a load of about 12000 kg. The overall density of thecomposite panels is about 32-46 wt. % lower than the density of thesteel used in the steel plates. The through-thickness electricalresistivity of comparative examples 6-7 is greater than 1×10¹⁰ Ω·cm,indicating that these panels have insulating characteristics. Thoughstampable, attempts to weld Comparative Examples 6-7 to a monolithicsteel panel results in structure that do not weld together. Thesesamples fail the weld test in that the weld is weaker than the panelsbeing welded together.

Examples 8-9

Examples 8 and 9 are composite materials prepared by compression moldinga sandwich panel using the method described for Comparative Examples6-7, except a core material including about 26.9 volume % of steelfibers and about 73.1 volume % nylon 12 is used. The steel fibers in thecore material have an average diameter of about 3-10 μm and an averagelength of about 2-4 mm and are mixed with the nylon 12 in a BrabenderPlastograph mixer at about 260° C. The thickness of the core material isabout 0.40 mm and about 0.57 mm for Examples 8 and 9, respectively.These samples are illustrated in Table 2. The overall density of thecomposite panels is about 29-36 wt. % lower than the density of thesteel. These composite panels are welded to steel sheet having athickness of about 0.8 mm using AC resistance welding (spot welding).Good welds (i.e., welds that are stronger than the panels being welded,such that a weld button is obtained when the welded panels are separatedby force) are obtained using a welding current of about 9.7 kA and 8weld cycles, with a pressure of about 600 psi. These conditions arelower than those required for welding two monolithic sheets of 0.8 mmthick steel (12.9 KA, 15 weld cycles, 600 psi pressure). Each weld cycleis about 1/60 second and the welding parameters include a slope of about1 cycle (i.e., about 1/60 second), a hold time of about 10 cycles (i.e.,about ⅙ second) and a squeeze time of about 1 second.

TABLE 1 Comparative Comparative Example 6 Example 7 Metal Plate 1Material Steel Steel Thickness, mm 0.20 0.20 Metal Plate 2 MaterialSteel Steel Thickness, mm 0.20 0.20 Core Material Thickness, mm 0.300.44 Thickness, vol % of total 43% 57% Metal Fiber, volume % of core  0% 0% Nylon 12, volume % of core 100%  100%  Total Density, g/cm³ 5.374.27 Weight Saving, % 32% 46% Core Layer Resistivity, Ω · cm >10¹²  >10¹²   Weld Properties Fail Fail

Examples 10-11

Examples 10 and 11 are composite materials prepared by compressionmolding a sandwich panel using the method described for Examples 8 and9, except the metal plates have a thickness of about 0.30 mm each, andthe samples are prepared with thickness of the core material of about0.39 mm, and about 0.54 mm, respectively. These samples are illustratedin Table 2. The overall density of the composite panels is about 25-30wt. % lower than the density of the steel. These composite panels arewelded to steel sheet having a thickness of about 0.8 mm using ACresistance welding (spot welding). Good welds are obtained using awelding current of about 9.7 kA and 8 weld cycles, with a pressure ofabout 600 psi.

TABLE 2 Example 8 Example 9 Example 10 Example 11 Metal Plate 1 MaterialSteel Steel Steel Steel Thickness, mm 0.20 0.20 0.30 0.30 Metal Plate 2Material Steel Steel Steel Steel Thickness, mm 0.20 0.20 0.30 0.30 CoreMaterial Thickness, mm 0.40 0.57 0.39 0.54 Thickness, vol %   50%   59%  39%   47% of total Metal Fiber, 26.9% 26.9% 26.9% 26.9% volume % ofcore Nylon 12, 73.1% 73.1% 73.1% 73.1% volume % of core Total Density,5.61 5.04 5.91 5.55 g/cm³ Weight Saving, %   29%   36%   25%   30% CoreLayer 910   480   <150    170   Resistivity, Ω · cm Weld Properties GoodGood Good Good

Examples 12-13

Examples 12 and 13 are composite materials prepared by compressionmolding a sandwich panel using the method described for ComparativeExamples 6-7, except a core material including about 20.2 volume % ofsteel fibers and about 79.8 volume % nylon 12 is used. The steel fibersin the core material have an average diameter of about 3-10 μm and anaverage length of about 2-4 mm and are mixed with the nylon 12 in aBrabender Plastograph mixer at about 260° C. The thickness of the corematerial is about 0.37 and about 0.55 mm, for Examples 12 and 13respectively. These samples are illustrated in Table 3. The overalldensity of the composite panels is about 31-41 wt. % lower than thedensity of the steel. These composite panels are welded to steel sheethaving a thickness of about 0.8 mm using AC resistance welding (spotwelding). Good welds are obtained using a welding current of about 9.7kA and 8 weld cycles, with a pressure of about 600 psi.

The stiffness and density of Example 12 and a monolithic sheet of thesame steel material used in the metallic layers of Example 12, bothhaving a thickness of about 0.87 mm are measured in thethrough-thickness direction. Example 12 is expected to have a higherstiffness to density ratio than the monolithic sheet of steel.

TABLE 3 Example 12 Example 13 Metal Plate 1 Material Steel SteelThickness, mm 0.20 0.20 Metal Plate 2 Material Steel Steel Thickness, mm0.20 0.20 Core Material (Example 1) Thickness, mm 0.37 0.55 Thickness,vol % of total   48%   58% Metal Fiber, volume % of core 20.2% 20.2%Nylon 12, volume % of core 79.8% 79.8% Total Density, g/cm³ 5.43 4.70Weight Saving, %   31%   41% Core Layer Resistivity, Ω · cm 740   500  Weld Properties Good Good

Example 14

Example 14 composite material sample is prepared by compression moldinga sandwich panel using the method described for Comparative Examples 6,except Example 3 is used for the core material. This composite panelsample is welded to steel sheet having a thickness of about 0.8 mm usingAC resistance welding (spot welding). Good welds are obtained using awelding current of about 9.7 kA and 8 weld cycles, with a pressure ofabout 600 psi.

Example 15

Example 15 composite material sample is prepared by compression moldinga sandwich panel using the method described for Comparative Examples 6,except Example 4 is used for the core material. This composite panelsample is welded to steel sheet having a thickness of about 0.8 mm usingAC resistance welding (spot welding). Good welds are obtained using awelding current of about 9.7 kA and 8 weld cycles, with a pressure ofabout 600 psi.

Example 16

A composite panel having dimensions of about 340 mm×540 mm and havingthe composition of Example 12 is prepared using a compression moldingprocess. The composite panel is stamped such that sections of the panelhave a draw ratio of about 3. After stamping it is expected that thepanel is free of cracks and wrinkles and has a class A surface. It isfurther expected that the metallic fibers do not tear and the core layerdoes not delaminate from the metallic layers.

Example 17-25

Examples 17-19 are neat polymers and mixtures of polymers with stainlesssteel fibers prepared using the method Example 1. Examples 17-19 areprepared using nylon 6 with about 0 wt %, about 3 wt. %, and about 10wt. % stainless steel fiber, respectively for Examples 17, 18, and 19.The tensile modulus of the core material of Example 17 is about 3.3 GPa.When the steel fiber is added at a concentration of about 3 wt. %(Example 18), the tensile modulus increases by more than 17% to about3.9 GPa. When the steel fiber is added at a concentration of about 10wt. % (Example 19), the tensile modulus increases by more than 100% toabout 7.3 GPa. The nylon is replaced with a copolyamide and theconcentration of the stainless steel fiber is about 0% wt. %, about 3wt. % and about 10 wt. % for Examples 20, 21, and 22, respectively. Thetensile modulus of the core material of Example 20 is about 700 MPa.When the steel fiber is added at a concentration of about 3 wt. %(Example 21), the tensile modulus increases by more than 50% to about1160 MPa. When the steel fiber is added at a concentration of about 10wt. % (Example 22), the tensile modulus increases by more than 200% toabout 2280 MPa. The nylon is replaced with an ethylene vinyl acetatecopolymer containing about 19 wt. % vinyl acetate and about 81 wt %ethylene, and the concentration of the stainless steel fiber is about 0%wt. %, about 3 wt. % and about 10 wt. % for Examples 23, 24, and 25,respectively. The neat ethylene vinyl acetate copolymer (Example 23) hasa tensile modulus of about 40 MPa, an elongation at failure of about680%, and a toughness of about 36 MPa. When the steel fiber is added ata concentration of about 3 wt. % (Example 24), the tensile modulusincreases by more than 100% to about 110 MPa, the elongation at failureremains about the same at about 680%, and the toughness increases toabout 47 MPa. When the steel fiber is added at a concentration of about10 wt. % (Example 25), the tensile modulus increases by more than 400%to about 210 MPa, the elongation at failure is about 70%, and thetoughness is about 3 MPa. As such, in general this and other embodimentsof herein may be characterized by a tensile modulus of the filledpolymeric material (e.g., the material of the core layer) includingmetallic fibers that is greater than the tensile modulus of the filledpolymeric material (e.g., the material of the core layer) having thesame composition but without metallic fibers preferably by at least 15%,more preferably by at least 50%, even more preferably by at least about100%, and most preferably by at least about 200%.

Example 26

A composite sandwich sheet is prepared including low carbon steel facesheets and a composite layer including about 20 volume % stainless steelfibers and about 80 volume % nylon. The composite material is spotwelded to a metal sheet made of low carbon steel. The welding conditionsinclude a squeeze time of about 60 cycles (each cycle being about 1/60second), a slope of about 1 cycle, a weld time of about 13 weld cycles,a current of about 5 kA, and a hold time of about 10 cycles.

The weld joint is sectioned, polished and studied by microscopy,microhardness, and energy dispersive x-ray spectroscopy (EDS). FIGS. 3A,3B, and 3C are micrographs illustrating different regions and/ordifferent magnifications of the sectioned weld joint.

The EDS and the microhardness (Vickers hardness as measured according toASTM E 384-08) show that the carbon concentration of the first metalliclayer has essentially no variation (e.g., between regions 32, 40, 41,and 42), except for a small amount of stainless steel near the weld zone32. The EDS and microhardness studies show that the metallic region 38near the weld zone consists essentially of stainless steel (i.e., thesteel used in the metallic fibers). In regions near the weld zone, themicrostructure of the first metallic layer is representative of bainiteand includes ferrite. In other regions, away from weld (e.g., at thelocation marked by 40), the first metallic layer has pure ferritegrains.

Examples 27-34 Electrical Resistivity

Examples 27 through 34 are prepared by mixing steel fibers to athermoplastic using the steel fiber concentration shown in TABLE 4 in aBrabender mixer. The composite materials are then prepared by moldingsandwiches having 0.4 mm of the fiber filled thermoplastic layer betweentwo 0.2 mm thick steel sheets. The through-thickness electricalresistivity of the composite materials, as measured using AC Modulation,is shown in TABLE 4. All of the composite materials filledthermoplastics have relatively low electrical resistivity and all of theunfilled thermoplastics have relatively high electrical resistivity.

TABLE 4 Steel Fibers Electrical Thermoplastic (Volume %) Resistivity Ω ·cm Example 27 Nylon 0  >10¹¹ Example 28 Nylon 26.9 250 Example 29 Nylon20 250 Example 30 Nylon 15 270 Example 31 Nylon 10 300 Example 32 EVA 0 >10¹¹ Example 33 EVA 3 400 Example 34 Copolyamide 3 600

As used herein, unless otherwise stated, the teachings envision that anymember of a genus (list) may be excluded from the genus; and/or anymember of a Markush grouping may be excluded from the grouping.

Unless otherwise stated, any numerical values recited herein include allvalues from the lower value to the upper value in increments of one unitprovided that there is a separation of at least 2 units between anylower value and any higher value. As an example, if it is stated thatthe amount of a component, a property, or a value of a process variablesuch as, for example, temperature, pressure, time and the like is, forexample, from 1 to 90, preferably from 20 to 80, more preferably from 30to 70, it is intended that intermediate range values such as (forexample, 15 to 85, 22 to 68, 43 to 51, 30 to 32 etc.) are within theteachings of this specification. Likewise, individual intermediatevalues are also within the present teachings. For values which are lessthan one, one unit is considered to be 0.0001, 0.001, 0.01 or 0.1 asappropriate. These are only examples of what is specifically intendedand all possible combinations of numerical values between the lowestvalue and the highest value enumerated are to be considered to beexpressly stated in this application in a similar manner. As can beseen, the teaching of amounts expressed as “parts by weight” herein alsocontemplates the same ranges expressed in terms of percent by weight.Thus, an expression in the Detailed Description of the Invention of arange in terms of at “‘x’ parts by weight of the resulting polymericblend composition” also contemplates a teaching of ranges of samerecited amount of “x” in percent by weight of the resulting polymericblend composition.”

Unless otherwise stated, all ranges include both endpoints and allnumbers between the endpoints. The use of “about” or “approximately” inconnection with a range applies to both ends of the range. Thus, “about20 to 30” is intended to cover “about 20 to about 30”, inclusive of atleast the specified endpoints.

The disclosures of all articles and references, including patentapplications and publications, are incorporated by reference for allpurposes. The term “consisting essentially of” to describe a combinationshall include the elements, ingredients, components or steps identified,and such other elements ingredients, components or steps that do notmaterially affect the basic and novel characteristics of thecombination. The use of the terms “comprising” or “including” todescribe combinations of elements, ingredients, components or stepsherein also contemplates embodiments that consist essentially of theelements, ingredients, components or steps.

Plural elements, ingredients, components or steps can be provided by asingle integrated element, ingredient, component or step. Alternatively,a single integrated element, ingredient, component or step might bedivided into separate plural elements, ingredients, components or steps.The disclosure of “a” or “one” to describe an element, ingredient,component or step is not intended to foreclose additional elements,ingredients, components or steps. All references herein to elements ormetals belonging to a certain Group refer to the Periodic Table of theElements published and copyrighted by CRC Press, Inc., 1989. Anyreference to the Group or Groups shall be to the Group or Groups asreflected in this Periodic Table of the Elements using the IUPAC systemfor numbering groups.

As used herein the terms “polymer” and “polymerization” are generic, andcan include either or both of the more specific cases of “homo-” andcopolymer” and “homo- and copolymerization”, respectively.

It is understood that the above description is intended to beillustrative and not restrictive. Many embodiments as well as manyapplications besides the examples provided will be apparent to those ofskill in the art upon reading the above description. The scope of theinvention should, therefore, be determined not with reference to theabove description, but should instead be determined with reference tothe appended claims, along with the full scope of equivalents to whichsuch claims are entitled. The disclosures of all articles andreferences, including patent applications and publications, areincorporated by reference for all purposes. The omission in thefollowing claims of any aspect of subject matter that is disclosedherein is not a disclaimer of such subject matter, nor should it beregarded that the inventors did not consider such subject matter to bepart of the disclosed inventive subject matter.

1. A light weight composite comprising: (i) a first metallic layer; (ii)a polymeric layer disposed on the first layer; and (iii) a metallicfiber distributed within the polymeric layer; wherein the polymericlayer includes a filled polymeric material containing a polymer, thepolymer having an elongation at failure of at least about 20% at atensile strain rate of about 0.1 s⁻¹ as measured according to ASTMD638-08; so that the resulting composite material may be welded,plastically deformed at strain rates greater than about 0.1 s⁻¹, orboth.
 2. A light weight composite of claim 1, wherein the polymerincludes a thermoplastic polymer having a glass transition temperature,T_(g), greater than about 80° C., or a melting temperature, T_(m),greater than about 80° C.
 3. A light weight composite of claim 1,wherein the volume ratio of the polymer to the metallic fiber is greaterthan about 2.2:1.
 4. A light weight composite of claim 3, wherein thecomposite comprises a second metallic layer, such that the polymericlayer is a core layer at least partially interposed between the firstmetallic layer and the second metallic layer; and the thermoplasticpolymer includes a polymer selected from the group consisting ofpolypropylenes, acetal copolymers, polyamides, polyamide copolymers,polyimides, polyesters, polycarbonates, acrylonitrile butadiene styrenecopolymers (i.e., ABS), polystyrenes, ethylene copolymers including atleast 80 wt. % ethylene, and any blend or combination thereof.
 5. Alight weight composite of claim 3, wherein the thermoplastic polymercomprises a polymer having a crystallinity from about 20% to about 80%.6. A light weight composite of claim 3 wherein the filled thermoplasticpolymer is characterized by a strain hardening modulus, G, which isgreater than about 1 MPa; an extrapolated yield stress, Y, which is lessthan about 120 MPa; a tensile modulus greater than about 750 MPa; anengineering tensile strength or a true tensile strength of at leastabout 25 MPa, or any combination thereof.
 7. A light weight composite ofclaim 3, wherein the thermoplastic polymer is substantially free of anyplasticizer.
 8. A light weight composite of claim 3, wherein themetallic fibers are characterized by a weight average length greaterthan about 1 mm; a weight average diameter from about 1.0 μm to about 50μm; or both.
 9. A light weight composite of claim 3, wherein themetallic fiber includes one or more metallic fibers selected from thegroup consisting of metallic steel, stainless steel, aluminum,magnesium, titanium, copper, alloys containing at least 40 wt % copper,alloys containing at least 40 wt % iron, alloys containing at least 40wt % aluminum, alloys containing at least 40 wt % titanium, and anycombination thereof; and the metallic fiber concentration is less thanabout 20 volume % based on the total volume of the polymeric layer. 10.A light weight composite of claim 3, wherein the filler includesreclaimed metallic particles or reclaimed metallic fibers which areproduced from offal recovered from a stamping operation.
 11. A lightweight composite of claim 4, wherein the first metallic layer comprisesa first metallic material selected from the group consisting of steel,high strength steel, medium strength steel, ultra-high strength steel,titanium, aluminum, and aluminum alloys; and the second metallic layercomprises a second metallic material selected from the group consistingof steel, high strength steel, medium strength steel, ultra-highstrength steel, titanium, aluminum, and aluminum alloys, wherein thefirst metallic material and the second metallic material are made ofdifferent metallic materials.
 12. A light weight composite of claim 4,wherein the first metallic layer comprises a first metallic materialselected from the group consisting of steel, high strength steel, mediumstrength steel, ultra-high strength steel, titanium, aluminum, andaluminum alloys; and the second metallic layer comprises a secondmetallic material selected from the group consisting of steel, highstrength steel, medium strength steel, ultra-high strength steel,titanium, aluminum, and aluminum alloys, wherein the first metallicmaterial and the second metallic material are made of the same metallicmaterials.
 13. A light weight composite of claim 4, wherein thecomposite is i) substantially free of epoxy; ii) substantially free ofpolymeric fibers; iii) substantially free of an adhesive layerinterposed between the polymeric layer and the first metallic layer; iv)or any combination of (i) through (iii).
 14. A light weight composite ofclaim 4, wherein the composite includes an adhesive layer interposedbetween the polymeric layer and the first metallic layer, wherein theadhesive layer includes a metallic fiber, a conductive filler particleselected from the group consisting of metallic particles, carbon black,graphite, iron phosphide, or any combination thereof, or both.
 15. Alight weight composite of claim 4, wherein the composite is capable of adraw ratio of at least 1.5 in a stamping operation.
 16. A process formanufacturing a composite material of claim 1, comprising the step of i)depositing the metallic fiber and the polymer for forming the polymericlayer that is bonded on the first metallic layer.
 17. An articleincluding a composite material of claim 1, wherein the article includesat least one weld that attaches the composite material to at least onematerial selected from the group consisting of a steel, a metal otherthan steel, a substantially identical composite material, a differentcomposite material, and any combination thereof.
 18. An article of claim17, wherein the composite material includes at least one stampedsection.
 19. A filled polymeric material comprising: i. a polymer, thepolymer having an elongation at failure of at least about 20% at atensile strain rate of about 0.1 s⁻¹ as measured according to ASTMD638-08; and ii. a metallic fiber distributed within the polymer;wherein the polymer includes a thermoplastic polymer having a glasstransition temperature, T_(g), greater than about 80° C., or a meltingtemperature, T_(m), greater than about 80° C.; and the volume ratio ofthe polymer to the metallic fiber is greater than about 2.2:1; so thatthe filled polymeric material is formed into a polymeric layer that maybe adhered to at least two metallic layers to form a sandwich compositesuch that the resulting composite material may be welded, plasticallydeformed at strain rates greater than about 0.1 s⁻¹, or both.
 20. Asheet of material comprising the filled polymeric material of claim 19.